Check out a Scott CR1 Pro as well. The carbon frame is better than the Trek or Spesh (IMP technology is basically smooth interior walls, which have a similar effect to butting steel tubes, and the only other companies that do this really are Time and Lightspeed [I think the Cannondale SuperSix Evo has them too]), it has a complete 6700 group set, and Ksyrium Elite wheel set. Plus, it goes for about $3500.
If you're set on the Roubaix or the Trek, I'd say get the Roubaix for the simple fact that wheels are going to be nicer.