I think it's a mistake to go purely by your height when considering buying a bike sight unseen. Bike fit isn't just about standover clearance - more important to your overall comfort on the bike is the top tube length. Everybody has different relative body dimensions - some have longer legs and shorter torso, or longer arms, or shorter legs and long torso, etc. The top tube length will determine how stretched out or scrunched up you are in the saddle, and that aspect is what will affect you most when spending long days on the bike. If you're too stretched out then you'll be putting too much weight on your hands, too scrunched up and you'll never feel like you're getting the power you should have on the hills. When I was shopping for a Long Haul Trucker a few years ago, going by my PBH on the online charts, I should have been on a 58cm or even 60cm. But when I went to do some test rides, I found that those were impossibly stretched out for me. I ended up on a 56cm, and even that had to have a 90mm stem just to make it work. A couple of cm here and there on a frame may not sound like much, but it makes a big difference - don't assume you can fix it with a different stem, because that changes the handling of the bike. If the stem is on the shorter side (90mm or less) then handling becomes more twitchy. It's best to find the right size frame from the start. The best thing to do would be to determine what distance you like to have on the top tube, and if the online bike matches that, and the standover is good, then you stand a good chance of making it work. Go into it with those two numbers, not just your height, otherwise you may be in for much wailing and gnashing of teeth (and selling on craigslist at a loss) once you get it built up and go on your first ride.
Neil