Well I do not buy it 120 mph out of the box come on!!!!
I have 2 turbo Vipers and the 15 XTX is stock motor no shim with EVO flash to pull timing and raise rev limit to 9700 RPMS. It has a MPI Stage I with 4th injector, upgraded fuel pump tons of clutch work and machining all done and tuned by Ulmer on the Dyno. It is geared at 24/46 with 8 tooth 3.0 driver with a theoretical top speed of 135.3. It dyno's at 227.5 hp at 7#'s of boost and 253.7 at 10.5#'s of boost. I never got a chance to run it at 10.5 #'s (was still in break in) but would only do 118 at 7 #'s. The 14 is still at Ulmer's being built into a monster Hoping for 360 hp and top speed in the 140's
My 15 with full compression makes a ton more hp at 7#'s than the 14 did at 9#'s after the rebuild with wiseco low compression pistons. Taking compression away lowers the gain from the turbo and also loses low rpm acceleration until the turbo spools
When my 14 was first boosted I ran with YamahaTim who had an identical setup in his LTX by the same builder (Hauck) and mine was faster from bottom to top every time we ran and back then top end was 108.
Here is my problem with his quote below:
They say they changed to a forged top gear that is nice but until this year I was running over 250 hp on the powdered metal set that came in the sled with no problems. most failures were bearing and chain failures do to them miss-printing the owners manual for setting chain tension and we all had a mess with the 14's till the reverse detent recall was implemented.
Then he states that a slide was shown how the warranty claims were greatly reduced since the 14's came out? How is this possible? maybe cause they are ignoring them? cause I can tell ya the starter failures in 15 were way more costly than the hand warmer failures and the blown motors due to factory approved turbo's was way more costly on the 16's
"Now the chain case has also been questioned – is it the same as the Viper? Yes and no. The chain case received a major redesign for the Viper to meet our QA. The spring loaded tensioner was changed to a fixed bolt adjuster, the jack shaft was changed to accept our secondary, the gear / chain supplier was changed to Borg Warner and various bearings, faces and bits addressed. For the Sidewinder, further upgrades have been made. The top gear material has changed from a powdered metal to forged machine sprockets for additional strength and the chain width is increased to 15 link (plate) from 13 link. We have had no failures during our durability and calibration testing. Zero. I didn’t attend the recent Arctic cat dealer meeting but a little birdie told me a slide was presented that showed some very significant decreases in their warranty costs since 2014. Make of that what you will. - See more at: http://snowmobiles.yamahablogs.ca/#sthash.8qPcYwGo.dpuf"
Do not get me wrong I love my Vipers and do not plan on going to anything else soon. After tons of work and $$$$ I have what I believe is one of the fastest trail sleds out there that can still play in Yellowstone powder. The 14 hopes to be one of the fastest on ice, snow and grass in 660 ft in its category and will still be trail worthy with a shock change!
But I can tell you I have less $$$$'s in the 15 completely done even adding in the price of a the turbo and have more hp than the sidewinder, you know as well as I do there is no replacement for displacement 
Ill drink a pile of Jack for you.
