I just recently decided to run some experiments on my 1983 Fuji S12S Ltd. I've been riding 700x32mm tires for quite a while. First with Schwalbe Marathons, then with much lighter Panaracer Paselas. I was having some troubles with the VO hammered fenders fitting properly, so I removed them and noticed how much space I still had. Now's the time to experiment!
I borrowed some of southpawboston's 650b wheels with hetres and they fit perfectly:
I'm still not sure if on a bike that big, the 650B wheels look too small, but I really enjoyed the 42mm wide tires when doing some gravel riding. Unfortunately, using the Tektro R556 55-73 mm Reach Brakes full extended didn't provide anywhere near enough stopping power for my comfort. In the end, I may someday get a 650B bike, but this Fuji wasn't going to work in that configuration for the kind of riding I wanted to do.
Still on a quest to see what i could fit, I went over to Harris Cyclery and talked to Jim the mechanic there, and together we tried on the 700x37mm Paselas. And they just barely fit! But boy are they comfortable. I've not yet ridden them enough to determine if they are much slower or if there are disadvantages to them.
700x37c paselas on the FUJI s12s! by
JPTwins, on Flickr
There is zero extra space for fenders, so this will probably be my summer dirt road riding setup (for D2R2 and such), after which I'll probably go back to fenders and 32mm. But I just wanted to put this out there, since I'm always searching for information like this.