Just saw this thread.
As Woodchuck said, I have a set of Tatou 4s on a 700 Yamaha. I have used them for the last 3 or 4 winters and will say that the 700 is about the minimum for power....especially in wet snow. The previous owner of mine had a clutch kit put in it, but you can still smoke the belt if you are not careful. It will go just about anywhere even with 2 people on board.
On mine, the odometer is off with the tracks on...it will read 10 miles traveled when you have only gone 6. Mine has power steering, but there are times when you can not turn the handle bar....have to see-saw back and forth to turn around. Good rig for looking for cat tracks tho'