Go to the newsgroup rec.sport.snowmobile and post your questions. There are many there that have the 4 strokers, all brands. IMHO the Yamaha has the edge on the others, thier HP is way more than the others.
I have never owned a Yamaha and probably never will unless I would get a 4 stroker. I have a Polaris Indy 700 and an Artic Cat 700 mountain cat so you know this isnt a biased post.