I agree, top tube length really is the more important factor. Standover clearance doesn't really matter once you're actually moving on the bike. Try putting in your measurements at the Competitive Cyclist fit calculator (http://www.competitivecyclist.com/za...LCULATOR_INTRO) and see what top tube it recommends.

If you really are exactly between two sizes, I'd err on the side of the smaller frame because it's easier to make a small bike fit a bigger rider by swapping different bits, than make a big bike fit a smaller rider. But really, you should try out some bikes to see what fits you best. I recently bought a bike and I also fell just about exactly between sizes according to the charts, but after shopping around and trying out a number of bikes at different shops it was clear that the smaller size was obviously a better fit.