The above comments are spot-on. I used the fit calculator on the competitive cyclist website (they have illustrative videos) and went with the "Eddy Fit", which they describe on the site. The fit calculator put me within perfect range for the 55cm kilo on all measures except seat tube length/standover clearance. As already stated, keep in mind that this dimension of sizing loses importance when you're actually riding the bike, although it does influence relative handlebar height at a given saddle height position. Anyway, I wanted a cockpit that offered a good compromise between comfort and aggressive stance (Eddy Fit), so I placed more importance on top tube length. Also, standover clearance issues were diminished by the fact that I wasn't wearing shoes during my inseam measurement, but I do wear cycling shoes when I ride. Just lean the bike over a little when you're straddling the top tube.

Bottom line is that I didn't guess on frame size, and I didn't just use standover clearance to determine size. I measured myself properly (my patient, loving wife helped) and am happy with my purchase.