Our riding area is a lot like yours, we ride high desert, mountains, and very rocky technical trails in Tecate B.C. I had a YZ 400 for a couple of years and I really liked it, I kept it stock except for revalving F&R. I never liked the steering in the tight stuff. great motor. I then got an '01 400 EXC and across the board....I like it better probably than any motorcycle I've ever owned, it does everything well. Lately I have been riding an '01 300 EXC, everything the YZ 400 isn't, the 300 is. An amazingly capable motorcycle with an engine that will get down and drag you through even though you did it wrong, and will get up and run with the best of the open classers. I can't find fault with it either KTM. I have a hard time deciding which bike to ride. I would say that the 300 EXC will outperform the YZ 400 in every way, you can't go wrong......Light, fast, strong, forgiving, and starts first kick everytime!