If you are buying a 2 person touring sled and you want to go 4 stroke then i guess it would be fine, but to echo charlie's words if i was buying a 4-stroke anything i wouldn't consider anything but a yamaha.
I wouldn't even think about getting a 4-stroke snowmobile unless it was yamaha. I know some like them, But with the new 2-strokes on the market they make 4-strokes obsolete before they even arrived.
Get a ski-doo 600sdi rev-based touring or performance sled and you won't be able knock the grin off your face with a cannon. I have owned 3 600sdi ski-doos for the last 3 years and logged over 15,000 miles (YES, FIFTEEN THOUSAND MILES) on them they are perfect! i have multiple sets of springs that i change during the season based on the amount of weight i am carrying, like when i take my wife along usually 2500 miles each year or if i am carrying lots of gas or whatever and it performs flawlessly all the time, and also in the last 3 years i havn't even opened the hoods on the machines except for a blown belt maybe once a year, and to add oil.
i get 12-20 miles per gallon depending on what i am doing. if i have 2 on the sled and we are really tearing it up, like the day last year we did 382 miles with 2 on the sled in 1 day. we got 12 mpg. if i am alone i get 19-20 and regular with 2 around 14 mpg. my alone avaerage is 17mpg.
also can reach 100mph with 2 on board or cruise at 20mph all day. smoothest engine on the market.