Yeah, I'd probably go with the 5w50 instead of 0w40 M1, if I go that route. I didn't realize they have a 5w50. Lots of guys on ATV forums run 0w40 M1. Is the 5w50 new?
I just saw Polaris has an extreme duty 10w50. I may consider that, too. I'll do some snow plowing and winter running with mine, so while it is more of a hot weather oil, it is rated from 0 degrees f to 130. My Rzr is stored in a garage that won't go below 55 degrees, so it never experiences temps low enough to worry. Truly, though, the Polaris 5w50 would be fine for me. While I run occasionally in the heat of summer, I don't really stress my ATV engines. Snow plowing may be the hardest time on them.