True, the measured height is what you expect it to be -- i.e., the c-c -- whereas the spec'ed frame size is the same or a bit bigger in recognition of the longer headtube and consequent taller stack height.

From what I see from the specs, CAAD 10, at least in my size, looked to be more in the classic style due to its horizontal top tube and short wheelbase but, for at any given size, it also has a longer headtube than the old classic stealies, which puts it more toward the comfort/endurance geo.

Consequently, if there is a standover issue or for those who may want an shorter headtube because they prefer a more aggressive riding position than the comfort/endurance geo will allow, it looks like you may need to go down a size.

The measured height of a nominal size 56 CAAD 10, C-C, is around 54 cm. I don't think that's comparable to classic, horisontal top tube geometry, which is why the nominal size has nothing to do with the measurement of the seat tube. For what it's worth, CAAD 10 has a fairly aggressive geometry if you compare the top tube to head tube length (or reach to stack). If you compare the head tube length to older bikes, you have to take into account the headset stack difference - Cannondale uses integrated headsets that add around 5 mm to the headtube length, while the conventional threadless and threaded headsets add 20-30 mm.

OP is 4" taller than you, so your situation differs significantly..

The OP was considering a size 52. So although my situation differs significantly, it does offer some perspective due to the fact that I feel good on my size 52 CAAD 10.