Why do you want such a tiny bike with a 31" inseam? I have a 32" inseam and ride a 56-57cm. Disregard ALL the advice you get insisting you have some magical minimum amount of crotch clearance over the top tube. This is a completely incorrect way to determine frame/bike size!
Follow the Fit Kit or Lemond (or others like Wrench Science) fit advice to determine your ideal bicycle dimensions. Don't sacrifice fit for clearance over the top tube. Although top tube clearance is nice to have, I'd rather have a bike that fits me while I'm RIDING it. People say, "What about if you hop off all of the sudden or crash?" Well, I don't spend much time just standing over my bike. When I used to line up for a race, I'd rest my thigh on the top tube with one foot clipped in and the other on the ground. And if and when I crash, I have lots more to worry about than the top tube! Hitting a tree, car, or whatever at 30mph is what I'm worried about! The top tube is the least of my worries.
That being said, the compact road frame design offers good fit with additional top tube clearance. That should make a lot of "aggro" mountain bike riders out there happy.