I had the same concern at first. I wanted to get into road biking, but wanted to get a decent older bike used rather than an expensive LBS bike so having the LBS fit me wasn't really an option. My first bike was one I could barely stand over... top tube does push the man parts slightly and the flutes on the seat post are barely showing. Since that bike I have gone down one size, and then down an additional size... First was 23" frame, then I bought a 22" and 21". I think they all feel absolutely fine. The 21" doesn't feel small in the slightest so I could probably go even smaller. You can always extend the seat higher, and stem (all mine are quill) so basically anything shorter than nut-cruncher seems to fit fine for me.