The six carbon is a great bike, I wouldn't take it out of your lineup completely. I would probably stay away from the six 5 though. The CAAD9 is most definitely the better bike vs the Six 5. If its the matter of a smooth ride, a nice set of tires with lower psi on the CAAD9 can make all the difference you'd need. If its the matter of liking the longer headtube of the six, just don't cut your fork down on the CAAD and ride the stem flipped up and the position will feel pretty damn close. If you tested and really liked the CAAD9, I'd say go for it. Check to see if you have other Cannondale dealers in your area though. It's always good to test your options. Good luck in the search.