A 49? I'm 5'9 and ride a 50cm.
Granted, it's slightly small, I still feel comfortable on it. Fitment calculators peg me for a 49cm; I always thought that sounded ridiculous, but after logging hundreds of miles on a 52 and a 54, I had an epiphany that the 50 suited me best.
Thanks for the advice, I really appreciate it. I'm thinking I'm just going to stick to a 43cm frame. The Windsor has a 28cm standover height, which should work out perfectly for me. From what I've been told at my LBS, the smaller the better.