I'm going to go a little against the grain here. First, I buy tons of stuff on ebay. Most of my bike, Harley and sailboat stuff I get there. I research until I'm comfortable that the item is what I want and buy (or win) it. Second, I'm 5'7" and ride a 19" which should be way too big by normal standards. I'm a roadie at heart and have done thousands of miles over many years on road bikes. But, I don't do any real hard off road riding. I wanted to get down to one bike that I could ride hard on the road, get good workouts, and take off occasionally through the woods if I feel like it. On the too big frame I feel more like the fit I would have on a road bike. I like that way. Sounds like this might be what you're after also. Good luck.
SS