Originally Posted by
Oldpeddaller
... my own preference is the Panaracer Pasela Tourguard. However you get a wider choice of wheels if you go for 700C. ...
I really like Paselas also, but I find I prefer the ride of the standard tire over the Tourguard version.
Generally speaking, there are less issues swapping form 27" to 700c than the other way around (clearance definitely won't be an issue, and it's usually easier to find longer reach brakes than super short ones).