Let's face it, Fred: we just don't walk around carrying swords these days. Tends to stop traffic & gets the gendarmes in an uproar. Swords don't even help much with road rage 'cause cars will win every time.... Sword speed isn't "of the essence" right now.
Most iaido waza today are taught not only for understanding the specific ryuha principles, but also for developing one's own timing, pace, & zanshin. Watching Yamazaki-Sensei in the YouTube clip you posted earlier (
http://www.youtube.com/watch?v=GUN3QLq13kI ), Fred, it's pretty obvious that almost any iaidoka with a year or two of practice can perform Seitei Gata a lot faster than he does. But I sincerely doubt that many of us will ever have the same level of understanding & zanshin. Just being able to perform faster doesn't equate with better.
As far as different speeds intrinsic to a specific ryuha, I'm willing to wager that what is taught by today's Sokes is not particularly closely related to what was taught a few hundred years ago. TSKSR may be the exception, but I wouldn't bet that way. Speed may, indeed, be a function of how close the battlefield is, but it would be difficult to tell for sure without a time machine....