Run your Artic cat oil, it will not cause you any problems, thinner or not it doesn't matter once diluted with gas. Snowmobiles are much harder on bearing than a bike, while the rpms may not be as high they are sustained for essentially the whole ride. I myself use phillps INJEX oil in my snowmobiles and in my motorcycles as well, I've been using it for years, it burns clean lubricates well, My 2t 125's and 250's turned much higher rpms than a k5 and never had an oil related failure. look on the container, if it is TC-WIII you can run it in your bike with no troubles. Back in my younger days I ran yamalube, I ran out and my dad had Artic synthetic oil, so I used it, I swear my machine had 10 extra horsepower (OK maybe it just felt like it)