Well he didn't specify, so I s'pose it can be in whatever gear you like. Freewheeling I can get er up to 48 for a couple of minutes downhill. Even if we assume he's talking fixed in a normal street gear though, I fail to see what the ability to spin fast has to do with having the ability to gauge frame stiffness. I'm more likely to notice flex mashing up a hill at 6mph than I am spinning downhill or on a flat, and if you can't spin smoothly, you can't hold top speed, so not only is it an ariitrary measure, it's the basss ackward one.