I'm 5'7" with about 30" inseam measured floor to the very top of the inside of my thigh.
The frame is a 54cm, which was the one and only R3 they had in stock.
My current Cannondale is a 54cm with 54.5cm top tube and a 90mm stem. Looking back, I should have gone for the 52cm with a longer stem, and if I were to pick up a Cervelo, I'd be getting a 51cm frame.