I have riden but frames. The Trek frame I put about 500 miles on and I have to say it is dead. You get no road feel from the Trek. The Cannondale frame was not a Caad 4, it was about three years old Caad. The Cannondale had a very harsh ride and was a great sprint bike(no flex). Both frames will weigh about the same. I would say if I had to choose between the two I would go with the Trek, I love carbon, it would not be my frist chose. I have heard go thing about the new Caad 4 frames, I hope to get a ride on one soon. I think it will also depend on how the bikes is built, fork, wheelset, and groupo will all make the bike feel different. Good luck.