A 56 cm bike might fit.

Basically, fit is one of those thing you can only get a feel for by riding a lot of bikes. I'd hold off on buying any bike you can't test-ride until you get a good eye for what kind of frames will fit you.

I think most people eyeball frame size from the headtube of a bike--it's the easiest place for me to check, in any case. After a month or two of obsessively looking at C&V picture threads and riding a bunch of potential craigslist bikes, you'll be able to tell pretty decently if a frame will fit just by looking at it. Some bikes have strange geometry that can't be accounted for, but when you're talking about size differences that small, you can usually kludge a decent fit with a combination of stem, saddle and seat post adjustments. Or you can just re sell the bike.

ETA: Compounding the difficulties is that many manufacturers don't even measure the same distance. Some Measure seat tube C-T, some C-C... And even then, you've got scalloped seat tubes, extended seat tubes, modern compact geometries... Awful, right?