Ugh. I'm going to disagree a bit with others here. Fit matters. A lot. Obviously, there is some wiggle room, but how much depends upon the bike and on your body. If you are on a bike that doesn't fit right, you absolutely will pay for it in some level of performance, either in handling or putting power to the pedals. Enough to bother you? I don't know, maybe not. I will say that there's a lot more you can do if the frame is a little small for you. That's usually fine. End up on a bike that's too big and, trust me, you're basically screwed. You can get it to work well enough, and I did this with a too-big frame for years. But you won't live up to the bike's potential or your potential on it. My advice would be: unless you really know what you're doing (and if you have to ask, you probably don't), why take a chance? If you get a screaming deal on a bike that doesn't really work for you, that's not actually much of a deal, is it?