As the bike is currently geared (13/48) it matches what I run on my '06 in desert races. I would think that something in the range of 13/49-51 would be more suitable for MX, but gearing is not a matter of matching the top speed to the track, it's about having "the right gear" in as many situations as possible. If you find yourself thinking you need a lower or higher gear for the approach to a particular jump at a particular track, but the next available gear in the trans is too big a correction, then you should try to change your gearing for that track. You also need to consider what the gearing change will do to or for the bike everywhere else on the course, too. Sometimes going lower to solve your problem with a jump approach creates trouble coming out of some other turns, whereas going higher still cures the jump problem, but leaves you with a better option elsewhere on the track. Once you find the right setup for one track, you may also discover that it doesn't work at some other track, and you may have to use a couple of different setups depending on where you ride. Usually, the flexibility of the wide power curve of a big 4-stroke makes it so that an overall tallish gearing setup works well in a lot more places that it would with a 2-stroke. But I don't recommend you go any smaller than 13 on the front. 12's wear too fast, and they're harder on chains and chain sliders, too.