i have about 1000 miles on my carbon Synapse and love it. i don't think the bike will cause you to lose a town line sprint. If you look at the geometries of the CAAD vs. the Synapse, they are very similar...only 0.5 to 1 cm at certain dimensions.

If racing is in your future, get the CAAD. Remember, some of the pro tour guys are riding the Synapse SL in stage races due to a comfort advantage. Ride 'em again and go with your gut.

Hope this helps...probably not though