i was trying to decide over the same two sleds, and could't decide so got both, sounds great i know but now i have twice the headaches.
the xp is retarded on belts, my first one lasted 9 miles! but it is fixable, extra pin weight, fix the secondary adjuster, and maybee new primary spring. now for the nytro it needed just as much or more tinkering with the clutching to set it up, and it is going to need a new helix for it to work properly stock.
the hand warmers on my xp still work fine and there is a fix if they quit, the nytro warmers seem to be very cold even on the highest setting.
the suspension on the xp is killer stock. no complaints and im 275 lbs. the nytro on the other hand is horrible stock. it needs ohlins all the way around.
both sleds feel great sidehilling or carving cant feel any extra weight on the nytro, until it gets stuck. power wise they feel close on the trail, but as soon as you get in deep snow the xp will leave it badly, and it should has 15 extra hp and quite a bit lighter. i have a challenger extreme on my nytro, 16x162x2.5 and it is needed for sure unless you ride only trails.
the nytro would also benefit from a larger gas tank, still waiting for the trail tanks. if you turbo the nytro, Darkos tunnel dump exhaust sounds like the way to go, but for no turbo id be looking at a tunnel dump too, just so you can carry extra gas a little easier.
they are both nice sleds and to tell you the truth if you still want the xp i would wait till next year for some of the bugs to get worked out. the nytro is nice, just lots of extras needed to ride it, even without a turbo.
oh yeah and for all the bashing the xp got about how week it would be, there are a few tweaked nytros out there already too, so dont let the chassis strength sway you either.