I have both a CAAD10 and Supersix no-mod. Both are decked out in identical gear, Di2, Ritchey bars, stem and seatpost, Arione CX, same wheels and tires. I use the CAAD everyday and the Supersix for races only.
I find them both very stiff, neither 'harsh', but the Supersix a little more compliant. Both are cheap frames, but I prefer to train and bash around on Al rather than carbon.
I realize this is an old thread, but curious by this statement. I would have thought you would have raced on your aluminum frame and kept the carbon for your long rides. But maybe your team is sponsored and the carbon frame replacement cost isn't as great for you?