I can't comment on the SX, but I can comment on the gearbox. My bike is an '05 MXC, and has the same 1-4 gears as the bike you are looking at. I've actually got a complete EXC tranny on my bench waiting to go in, but the close ratio box has come to grow on me.
On the SX, it seems fairly common for people to swap in the EXC 5th & 6th. That gives you a close 1-4 for aggresive riding, then the taller gears when you are trying to cover some ground. Search KTMtalk; tons of info on this there.