Can you really feel the difference? I have had race wheels with just about every possible configuration over the years, from Shamals to regular 36h rims, and I can't tell a thing. Tires, for sure, but spokes not. Wasn't Sheldon just saying that because there's more weight and torque applied to the rear wheel, its better to have more spokes?

Back to the point, I have converted a couple of 27" bikes to 700c and if you use slightly bigger tires there's really no perceptible difference at all, except for a slightly more plush ride. One of my very favorite bikes is an old gaspipe Fuji 12-speed. Heavy, but immaculate build quality and a very handsome frame (horiz. TT, properly curved fork blades, etc.). Converted to 700c, found it had room for fenders, had some fender bosses brazed in, and it's just great. I think it has the 33.3333 Rivendell tires on it, which are good.