Lex Orandi...

hello,
good to hear from you. Our friend is mutual.
To start my piece "We" was intended to be poetical (regardless of it's "pseudo" appearance). I wrote it as a free expression of my state. The words were not contrived through some filter of "knowing" I was simply using poetry to express a more remote state of consciousness that I enjoy playing with. I am however willing to entertain the rigorousness that you seem to like to play with.
Also "art" does have meaning (at least depending on what theory of meaning you're willing to accept. I personally have a hard time arguing with Dummett and Wittgenstein when they deal with meaning as use).

"You make some authoritative, absolute statements, such as 'we have all been to the end of ourselves'".
Please define your intentions when you use propositions like "authority". I find it too confusing to deal with otherwise. We'd be here all night.
That being said I'm just gonna go for the gusto and assume I know what you mean by this. My authority comes from experience, empiricism, modern psychology and plain old intuition. The reason I didn't demonstrate my authority is because it was meant more as a game than a philosophical position (this was a work of verse not prose). On the more rigorous side of things, however, I literally meant that every person is always working in the best way they know how with the resources available to them at their current level of awareness. This is sound psychology (I'm sure I could find quotes and peer reviewed sources if you really don't believe me).
Interpreted another way (this is poetry after all and poetry does work on levels even if it is pseudo) I'm willing to say that I meant we all (at least on some level) know what we are and aren't capable of. This is a weaker interpretation however.

"I ask only by what authority you speak."
Again I'm not entirely sure what you're after here. I'll assume you just want some support for what I said. Consider the statement "we have all been to the end of ourselves." Let's interpret it in a new way, a more rigorous analytical way (then maybe we'll address a synthetic interpretation). It's not unfair to break it down into reworded sentences such as "for every element that is aptly called an element of Humanity (We) that element has an awareness, and that awareness necessarily entails an awareness of what the element is capable of being aware of(awareness of awareness isn't unreasonable). That awareness of capacity marks one of the limits of what the element can aptly call 'self'." Is this awareness the only thing that marks our limits? No not by a long shot. Does it provide a tangible limit that may or may not be useful for dealing with one's present circumstances? Yes. Put in yet another way: people never knowingly fuck themselves over. No one wakes up in the morning and says to themselves "I'm gonna make things hard for myself". It does happen that a person's self awareness and awareness of their surroundings and of reality in general is so distorted, generalized and incomplete (owing to a necessary function of the human brain to cope with the staggering mass of information presented to it every second) that that person works in an inappropriate way. That is not to say that they are not functioning in the best way they know how (at the end of themselves) it just means that, for whatever reason (environmental factors, genetics, habit, or just due to misunderstanding of the presence or nature of those deleting, distorting and generalizing faculties) that person does not know how to get the results they want or that they have distorted what they think they want into what they are use to, or to what they think works for others (a poor M.O.). Whatever the case the human condition, just as nature as a whole, is engineered to function efficiently and optimally. Consciousness is designed to give us choice (a great creative faculty) but in so doing it also opens up the possibility of making strange choices. That's not to say that those choices are not always in the form of optimality based on the subjective relation of the element to it's environment.

"How is it possible to quantify a statement such as this? What metrics are used in its apprehension?"
Do we really need to invoke metrics? It is possible. I'm sure I could lay out a formal proof with Venn diagrams or quantifiers or whatever if you'd like but I'd ask you first to let me know why such formality is necessary. As far as I'm concerned this will only provide an analytic proof, not very interesting. The synthetic support for this is much more appropriate to the task of translating my intent (at least attempting to anyway).

"Are you speaking of an absolute human condition?"
Poetically no I hadn't intended that. But I am, obviously, willing to entertain the possibility. Like I said above it is a common psychological position that human behavior (used in a very broad sense so as to include mental and emotional behaviors as well as conscious awareness) is constantly working at it's current relative optimality.
Now, you might have been questioning my ability to support the statement in the context of "absolute human potential". If that's the case I'm not sure how I could reasonably support that except by referencing the ever elusive entanglement principle of quantum physics. By invoking entanglement we can now discard the conscious realizations of any one individual and accept that humanity as a whole (as well as every other aspect of existence and the universe) is inseparable and privy to the awareness of any and every awareness that has ever been, both human awareness or otherwise. So we can effectively say that if you believe in the existence of a man like Jesus (or his ilk), and that such a man was privy to the consciousness of godhead (even in a remote way, whatever that may mean) then every other part of humanity is likewise privy (this I assume would be the limit of human potential. Unless of course you're either unwilling to acknowledge Jesus as either the hight of human potential or a human at all. Either way I'd love to hear your arguments for that;). The only difference between Jesus and Joe Slob is that Jesus acknowledged and used that consciousness. Joe Slob has only availed himself of this consciousness through Jesus and has yet to call it up into conscious awareness. That is not to say that he is unaware of what Jesus was aware of (Joe Slob has been to the end of himself just as Jesus had) only that Joe is using a more remote aspect of himself to do it than Jesus did. Entanglement is unable to differentiate between individual minds. It literally supports the notion of universal consciousness, ever present, all pervasive. No one is exempt. So if Jesus did it he did it as a result of Humanity as a whole, and also if you are willing to say that Jesus did then you must say that the entire human race did as well.
Yet another interpretation of my statement. Not a bad one either.

"Is it possible to know such while being a part of the control group?"
It is just as supportable to say yes as it is to say no. That being the case is it even worth discussing? Probably not so let's just say that I'm willing to say "yes it is possible." How would I support that? This is not like Wittgenstein's case of the eye that can see everything but itself. Humanity has an advantage that it can collectively reflect on it's elements and on the whole. It's called communication (we've also previously invoked Entanglement so we can reference that as well). What you are proposing is like saying that we cannot know anything absolute about ourselves because we can't see our own faces. We can however introspect about the whole of ourselves and our parts. Also there are mirrors all around, and friends. If the opposite were true you would have effectively demolished the entirety of psychology and possibly a large part of philosophy. How could psychology stand as even a pseudo-science if your proposition were consistent with reality? Also we really wouldn't be able to say much about Logic or Language, maybe even physiology, neuroscience, or biomechanics, the very concept of introspection would have to be dismissed, infact I'm libel to think that the mind in general would have to be dismissed as merely a pipe dream, something left for the musings of confused poets.
I'm a bit unsatisfied with my treatment of this section so pleas be as brutal as possible with this as you can (that goes for the rest of it as well). It's the only way I'll learn.:)

"To quote myself (because it is a good quote), given a large enough context, any field of human study encroaches upon itself."
It sure does (if I'm translating your intention properly). But the good thing about this is that such a broad perspective is only useful when considering holistics. A good thing to do and a whole heap of fun, but a bit inappropriate in this context. Context is important otherwise we'd all have to face this "encroaching" at every turn and I don't think that'd be too much fun. In most cases we have to abandon broadness in favor of usefulness. If we didn't we'd have to do away with philosophy (at least a large part of it) and I'd be forced to ask you to stop philosophizing about my poetry (something I'm not willing to do). Popper deals with this concept nicely when he deals with the infinite regress. Seems to me Dummett treats it in the same way.
(reviewing this I'm no longer convinced that we're dealing with similar concepts. I'd really appreciate it if you'd elaborate on this. It might be fun to explore this in more depth with your help.)