At 6' you should be either on a 56 or 58, with the 56 at the bare minimum. Really depends on your build at that height. 56 might be too small, 58 too big, you would really want to try it out before purchasing. Co-worker at the shop is 5'8" and rides a 54cm S-Works Langster. I took it on a spin. I look like Donkey Kong on that thing. At 6', I am all torso and have short legs. Even with a 130mm stem it probably still wouldn't fit me.

Standover is really worthless unless all you do is stand over your bike. I like a higher top tube so I can sit on the dang thing at the light while still clipped in and my other foot on the ground.