I went to check them out at Helen's Cycles in Santa Monica, CA. I rode a CAAD12 Ultegra first, then then salesman put me on a '17 SuperSix Evo Disc Ultegra that they were looking to shift for cheap (at first he said there was some "wiggle room" and when I didn't say anything he threw out $2300). Honestly, I thought the CAAD12 was a little more comfortable, but I think it was in my head because I'm pretty sure they have the same geometry.
Anyway, both bikes were super nice. I "felt" the aggressiveness more in my arms and elbows than in my back. If the SuperSix hadn't been violently neon yellow, I might've left with it.