In the FWIW dept. I just bought another vintage bike and the original 700c sew up rims had been switched out to 27's. The shop I bought the bike from put some Pasela Tour guards on it. Nice, but at 1 1/4, there was VERY little clearance. Almost none.
So, trying to keep the wheels I opted for Pasela 27 by 1 inch tires. Nice. Kind of low profile and narrow, looking much more like a "fat" tubular. Looks much better on a "racing bike" than the fatter tires, IMO.