Mtx is the way to go.

Long story short, Mtx Nytro hauls ass. When crossing over to the four-stroke side, some adjustments must be made. Sell your two stroke oil, buy a nice snowmobile suit that you can actually keep in the house, (no smoke from the two-stroke oil), and practice your hand strength. You will need to hold o...n to those bars! Downsides: reverse handle is too close to the body panel, so when its very cold, and the handle freezes in, it is impossible to get your fingers around it in order to pull and engage reverse. Tip: Pour a little methanol or anti-freeze down the reverse shaft to avoid having to heave the sled around old-school.
The torque of this thing is incredible. And the throttle response is like none other. Once I was used to the engine braking, I almost stopped using the brakes. When I picked it up from the Yamaha dealership, they tols me I should upgrade to a Piaa lighting system. I ride a lot at night, and the lights are plenty bright enough for all of the riding conditions I have encountered. Suspension is more than ample on both ends...and I have even gone two up,(not recommended), with no bottoming out. Good luck keeping the skis on the ground with two people and full throttle, though!
All in all, fuel economy, reliability, environmentally conscious and gobs of torque. I have only omitted deep powder riding because of the weird weather patterns this year.... I will update soon, and have utmost confidence in this sled. Read Full Review