Standover height doesn't mean squat. What really matters is cockpit length (ie - top tube length + seat tube angle = reach). I'm 5'9" and ride a 19" X-Cal 29er. Top tube is a little high, but the rest of the bike fits much better.

It probably really comes down to: do you want the bike to fit well or do you want to have a slight risk of racking yourself? Test ride different sizes to see what feels right to you...and get clipless pedals.