5'9" and I ride a 54. When I tested bikes, 56 felt just as good. But the shop owner talked me into a 54. Ergonomically, it's just a tad better fit.
My vintage Falcon that I acquired for free is a 60. I can ride it fine, but the nut rubbage bothers me. Not that I ever have both feet on the ground while straddling the bike, but still....