posted this in the fitting forum, but didn't really get a lot. i've always been under the impression that top tube + stem length (or frame reach + stem length) could be kind of interchanged (i.e. like a 54cm with 110 stem equals 56 with 90 stem). of course, all this assumes similar saddle/handlebar drop and most things being equal. i tried a 54 last week and as far as reach is identical to my current 56, and in a brief test ride felt like a better fit and more comfortable. i'd like to take one out for a longer test ride to see how it holds up over a normal ride for me, but i've been wondering if there is anything a shorter top tube that could be more comfortable for me compared to an equivalent reach and bar height on a bigger top tubed frame.

edit: there's probably too many other factors, from handlebar design to seat tube angle that I'm missing. so i definitely oversimplify here