the inseam calculation is really just a rough estimate for seat tube size. the range is .65 to .68 your inseam, and i usually calculate it as .665 [which gives you 57.2]. a centimetre either way wont really matter as long at the most important metric -- the top tube and stem length -- is right. basically, you want your top tube length to be long enough that you don't need a stem longer than 120 mm or shorter than 90 mm to feel comfortable. i'd say you should look for a bike with at least a 57 mm top tube and go from there.