I just picked up 4X, first time in my life a few months ago. Built up an 18" (I'm tall) Banshee Morphine, of course, as a SS. My 4th SS in a row after 3 Surly's (KM, Pacer, CrossCheck). Now running it 38-16, but that's a bit long for our local track, with a long double directly after the start podium, and a few tight hips. Looking for a good 34t 4-arm to put on my Saint crank, so I don't have to figure out a working rear wheel position all over again. Sad though, the 38-16 and fully extended Thomson post are great for rolling the 11 miles to the 4X track, 34-1 will be less of a joy I'm affraid. I really like 4X, will have to try it on some BMX tracks soon, too.