The reason I started thinking about old school gearing was when I watched this YouTube video of the 1974 Giro awhile back. At about 3:45 you get a glimpse of the drivetrain of a rider. I'm no authority on the history of gearing used by pros, but back then I'm guessing 42T was standard and that rear freewheel looks like it is 23T, maybe 25T max.

http://www.youtube.com/watch?v=8km8B7A0L9Y

42x23 never kept me from riding anywhere on my '88 Sirrus, so I figured I'd give it a shot again. 42x23 is the lowest gear on the Bianchi Nouva Racing frame I built up last year; I have 42x26 on my LeMond Buenos Aires and 42x25 on my De Rosa.