Don't buy a bike without test driving it. Different brands, and different style bikes have different dimesions. For instance, a 52cm touring bike is quite different from a 52cm TT bike. Have your bike professionally fitted to you. Your local bike shop will do this for free if you buy the bike from them, if you don't they'll usually do it for a fee between $40 and $200 depending on their methods. There's a fit shop out in AZ somewhere that is supposed to be awesome.