I have a 2004 Trek 5500 that came with a Race X Lite fork with minimal vertical clearance for the front tire as well. The fork would just barely take the old Conti Grand Prix 3000 tires in a 700*25, but it won't take a Grand Prix 4000 in a 700*25, which is several mms taller than the old 3000. So I run a 25 on the back and a 23 in the front.
Regarding your Specialized Pro Roubaix tire, here is what it says on the Specialized website: <<Comfortable large volume 25c casing, merged with fast-rolling 23c Dual Radius Tread (DRT) ensure a supple ride that rolls fast and corners extremely well, all in one tire.>> So I don't think that tire comes in a legitimate 700*23 size. It is probably a nice tire though. Too bad it won't fit.
Last edited by Skewer; 06-11-08 at 10:46 PM.