I have a Brute Force 650. It's been from sea level down here in Corpus, to well over 6000 ft in NM. I've literally flogged the heck out of it and never so much as a whimper. It has more than enough power to hit 65mph here in Texas, couldnt quite get there in NM, about 58mph at around 3000ft. Ive also been impressed by the stock tires puncture resistance. Alot of sharp rocks, and mesquite where I ride and no problems. The front tires suck in the soft stuff though. My only complaint is that the cooling system is adequate at best. Extended slow trail rides will get it hot. A few minutes at higher speed have proven to cool it down though. Oh, it will stomp my moms 660
grizzly in any drag race, although the Grizzly sure is a comfortable ride. just my 2 cents!