I would go test them out, starting with the taller frame first. You'll know immediately.
Though I'm heavy and far less flexible than I used to be, as long as the handlebar height, stem length, and seat (up/down + fore/aft) can be tweaked, I can pretty much set up a frame of 56cm +/- 3 cm to be comfortable.
Last edited by oddjob2; 07-23-12 at 10:35 PM.