The conventional wisdom around here is that you should avoid purchasing your first bike online (I haven't been around that long, but it makes sense to me!). Fit is a lot more complicated than simply matching your height to a frame size based on a generic table. I won't give you the full lecture since you've already read a few threads, but I'd recommend going for the larger size when you fall on the height border. It's a lot easier to adjust a slightly bigger frame to fit you than it is to adjust a slightly smaller frame. Just make sure you have sufficient standover clearance.