This is helpful - thanks guys. One more question. If I'm going to add aero bars, would that influence the size bike I should get, as opposed to if I was just getting a road bike to ride as a road bike? Seems like in the aero position I might be more stretched out. I've seen sizes 55 and 57 too, so I'm just wondering 1. would those work period if I should be looking at a 56, and 2. if I'm adding aero bars, would smaller (55, 56) be better than larger (57)?