Depends on what you're using it for. Out of the box they don't do very well... It took me a season to get mine setup (custom rider forward, tunnel extension, lightweight rear skid, 162 track, proper clutching, rejetting, ECP filters and Modded an r6 exhaust to work with the stock header) but now I pretty much keep up with any 800. Just takes some setting up.. The motor is like no other, the front end is VERY heavy in deep snow when stuck, but if you keep momentum it feels as light as just about anything... you can lighten up the rear pretty easy which helps getting it unstuck (mine is lighter than an xp in the back). Totallyamaha has a great forum dedicated to the old rx mountain and there are all kinds of tricks. You can get them pretty light for a minimal expense... and if you don't get crazy with boost the motors will last forever.
Keep in mind I'm a big dude, 6'4" 280. So I like a heavier machine, it's easier for me to throw around than a lighter one because of my leverage.
Believe it or not the "one ton" with my big *** can get airborne
Where I ride
Here's a vid of me climbing out of that same bowl (above) after haveing to turn out a few times from all the holes that where dug from sleds rolling. Had to side hill out of it... but it gives you an idea of what they're capable of if you can hold on for the ride! Sorry in advance for the crappy camera, my buddy had ice all over the lens and didn't know it.
http://www.youtube.com/watch?v=zqkbfobmjSg