Go ride some bikes in stores, but you probably need a 50 or 52. Depending on the geometry. When you test ride on that you like, make sure you remember what it is and what size, then you can look up the geometry on the manufacterer's website and compare the Bikes Direct bike you are looking at. Effective top tube length is most important and then head tube length.
When you get your bike make sure the cog and lockring are tight or you will strip your hub. Put the wheel on the bike, get on, lock up the brakes, and crank the pedals with all you've got. Then tighten the lockring (remember it's reverse thread). Check it again after the first few rides.