Another vote for riding both of them -- you can upgrade/switch out components if you want, but picking the wrong frame is a worse position to be in IMO. Only you will know which rides best for you - either is a sweet deal - you have a pretty nice problem on your hands. I ride a Roubaix comp w/105 and love it -- the bike is still plenty fast, it's just not as overtly race-oriented as the Tarmac. I ride lots of hills and like the flexibility I have with my Roubaix.