I run Schaeffer's Racing 5w50 with great results in my Scrambler 850 HO. I have also ran Silkolene 15w50 in the engine and got similarly good results. I think the Polaris engines aren't hard on oil, no more so that a normal car engine. Polaris engines don't have wet clutches or integral transmissions which means that the oil for the engine only has to lubricate the engine, an easier job for oil than other ATV applications. Take a look at Castrol 5w50 if you want an off the shelf product, it has better zinc and phosphorus numbers than the Mobil One 5w50. That being said, the Mobil One 5w50 is a fine oil and would likely work well. The Mobil One 15w50 has better zinc and phosphorus numbers and would be better IMO if you don't regularly ride in very cold conditions. Lots of people run 0w40 or 5w40 with good results they say, but I haven't seen an oil analysis of the lighter viscosity oils in a Polaris engine so I can't say for sure. I have a Ranger 570 that I am currently running Klotz ATV/UTV 0w40 oil in. The engine seems fine with it, but I haven't had it analyzed so I don't know how it's doing really.
Long story short, there aren't many 5w50 oils to choose from. All of them would likely work well in your Polaris, just pick one that's easiest to get and change it fairly regularly, maybe 50 hours of run time, more often if you ride in very dusty conditions.