JoeOxfordCT, You may shave a few grams with a smaller frame, you may end up using a longer steerer stem which may cause the steering to feel negatively different and you may spend bucks for something that's not quite right for you. If you're really just wanting a CAAD10 frame, buy one that you already know fits.

I think stiffness between two adjacent frame sizes would be unnoticeable. I ride 58 cm Cannondales, but I have a 56 cm crit Cannondale. The difference between the two is down to the head tube angle, crit bike is 1 degree steeper, wheelbase is shorter and it turns on a dime. The top tubes are within 1/2 cm between the two sizes, which allows it to fit me. A standard 56 cm frame's TT is too short... I've tried.

Brad