There are a couple of recent threads on bikes for 5'2" women that have good info on some of the issues with 700 vs 650cc wheels. BF people had some good comments about how the choice can affect frame geometry, tow overlap, etc. Even thought you're obviously not looking for WSD bikes, it may give you some insight into the geometry issues with smaller frames.

I don't know about used bikes in the $600-800 price range. However, in testing bikes for myself, (female, 5'3" and 29" inseam), I found that some of the Giant bikes seemed to have a longish TT compared with other bikes I tested. I didn't go for one of those because I needed a much shorter TT, but if you have a long torso, then it might be worth at least looking at their website. The bikes I looked at from Giant all had sloping top tubes however.