get a 56 or, 58 if standover allows it, then just get the shortest stem whith a big ol' 17degree angle flipped up, that should make it comfortable to ride.
If you're serious about buying when they put pedals on the bike, they should also be doing a quick fit of the bike, saddle height, and bar height so you can compare pretty evenly on fit, and just pay attention to road feel. It takes what? 3 minutes to flip a stem? Unless there's something overly wrong with how you fit on the bike that isn't correctable with a couple of adjustments, then don't buy a bike based on fit.
Buy based on ride, IE harsh, soft, smooth, twitchy, flexy, responsive, sluggish.
Oh and you should probably be holding the hoods (rubber ontop of the breaks) not the drops when you first sit on the bike, unless you're a track cyclist or sprinter. Most people don't use the drops for more then a couple minutes at a time to lead out a group. sprint, or on a really fast paced climb.