Small: Men's 6 - 7.5
Med: Men's 8 - 9.5
Large: Men's 10-12
X-Large: Men's 12 and up
I would try a large if you have a 12 and have that much space between your shoe and the clip. As for over lap, if it's only 1/2" you won't have a problem with a smaller clip. Also over lap is mostly a problem with slower speeds, the faster the speed the less likely it is you'll hit your front wheel.