Hmm, a counter point for the 52cm sizing.

I'm almost 5'7 and about 30.5" inseam. I've been riding my 2006 52cm C'dale caad8 for over a year with no issues (110mm, -10deg), with the saddle pushed almost all the way back. I've tried moving the saddle forward and that gave me leg cramps. I have also tried the 50cm and it felt a little cramped.