interestingly, the reach and stack of my bike are similar to the 54cm allez I tried (the allez does have a slightly longer headtube 14.5 cm vs 13 on mine, although I have a quill stem converter with some spacers). I didn't realize these until after the fact when I looked up the geometry and was quite surprised at my perceived comfort with it. I'm going to have to do some more test drives, and rent something if I can (although it seems like the only shops that have rentals here only rent out Giant).
What I'd like to get to the bottom of eventually once I can talk to a fitter is whether my discomfort on the bike (trapezius mainly) is a function of my fit (possibly, but I've tried to address the common symptoms of that with bar width, stem length, etc) or if it's a frame issue (mid 90's harsh aluminum where I feel my trapezius tighten over the more unavoidable parts of rough roads, and running slightly lower pressures doesn't seem to change it too much).