I have a 99 MXZ 600 and it does pretty well for itself. The rear suspension is pretty harsh for trail riding but it loves to nail the bumps. If I were you I would aim for a 2003 mxz 800 with the VR Shock. My buddy has on and it's an awesome sled to ride. Very comfortable. It Almost as fast at my 2006 mxz adrenaline.
If you can snag a REV chasis sled you will absolutely love it once you get used to it. I don't like the triples because of the chasis and suspension setups.
I haven't had a problem with the 99 or 03 that my friend rides. Just make sure you look it over and check out any wear. When you buy one make sure you clean the carbs
-Adrenalin