I think that the answer to David Skagg's question is complicated by the mental/emotional aspect of fighting. A student might have superb skills in the dojo, but not have the fighter's mentality that is necessary on the street. Another student might do poorly in the dojo, yet turn into a tiger when physically provoked. Perhaps the former student grew up in a safe neighborhood and has never been in a real fight, and the latter student grew up in a rough neighborhood and has lots of experience in street fights.
The questions in post #9 remain as to whether the student's aikido would be effective (ie., "adequate to accomplish a purpose") on the street. But a fighter would be foolish to limit himself to any particular sort of techniques (if for no other reason than this would give an advantage to an opponent who is familiar with the art the student studies). As George Ledyard wrote in another thread, "if someone comes through the door with bad intentions, that's a fight and it won't be pretty."
So I think that if I were to try to answer the questions in post #9, I would need to know more about the student than how well he (or she) performs on the mat.
In my combatives classes, I run drills that are designed to produce excessive stress and sensory/neural overrides in order to deal with this issue. You cannot sustain training by training this way all the time, but it is a very important part of training if you are training for real.