Personally, I do not see how lowering the top tube in any way makes a 54 cm 'virtual" bike fit more body sizes. The lowered tube with long seat post offers nothing that the classic square frame with a shorter seat post doesn't. When you get off the bike, you naturally drop the frame off to one side so that your dangly bits don't hit, even if you are a little small for the frame. I ride a 54 cm bike, but in a pinch I could use a 58 with a short stem, without damaging any minor organs. The handling wouldn't be ideal, but that would be the same case if top tube were dropped, raised or invisible. Nothing changes. If I ride a 55, I just lower the stem, and if I ride a 53 I raise it. If I ride a 52, my knees jamb into my ribs, and if I ride a 56 I can't get low enough in the drops. Three sizes fit all, assumes the rider doesn't ride much.
Garth Libre in Miami Fl.