Next week, I'm going in for a fitting at a local shop, and will be looking at both of these bikes. They're both 2010 models (great price break), and want to know of some of the pros and cons for each to keep in mind as I'm trying them out. Durability, common mechanical issues, ease of repair during a race, etc. If it matters, I've been riding a Trek 1.2 road bike for 3 years, and will be keeping that to use as my main trainer.
Most of your decision will depend on which one fits you best. Most high end bikes will be light, fast, and durable (see what the warranty is for both). If you crash a carbon bike hard you won't be able to repair like a steel bike. Mechanical issues will depend on how well you take care of the bike, particularly wheels and drivetrain. Campy, Shimano, SRAM? Also a bit of personal preference. Same with level of components. You don't get too much more bang for the bigger bucks of Dura Ace versus Ultegra, for instance. Repair during a race is almost always a flat tire, although I had a chain break once that took ten minutes to fix on a 200 mile race.