Wow. That's quite the change. Old geometry, I'd probably ride a 51 or 54. New geometry, the 54 would be almost too long (ideal reach on a road bike for me is 370mm or just under), and I could ride either the 48 or a 51. I'm 5'7". I should not be riding a 48cm bike. Also, the reach is identical on the 48 and 51, which makes no sense.