In my opinion this is a scientific question... I know its fashionable in virtually every forum regarding vehicles in general to alter make better or Uncle Jethro sayz if you use this particular brand you extend longevity so on and so on.
I guarantee you Polaris engineers and scientist have spent more hours than you or I can imagine developing the perfect oil for this product to run on. And I might add, in virtually every weather condition known on earth. Then they tear the whole power-train down and go over every part utilizing a microscope. If you still insist on running an alternative, then go ahead, its your machine, but in the event something fails, and you need Polaris to repair or replace, standby for the bad news. It takes nothing to send an oil analysis to a lab and get it identified. Same with stressed parts, so as to prove the alternate product caused the failure
I use my Polaris for fun, I have never used any other brand and do not plan on using any other lubrication product other than factory specified. I always figure I must pay to play, there is no easy solution to getting off cheaply with any of our hobby toys, rifles handguns, Jeeps they are all expensive and will always need... it takes $$$
As I advise, do what you will, but taking advice on a forum from unknown people with only Internet screen names putting your brand new machine at their mercy?
Only sayin' its not meant to be disrespectful of folks in here...
If you still wish to pursue Amsoil? Then you do the investigation and research and find out exactly how many man hours and by what means have Polaris 800's been tested, under what condition/s and so on? You want this in writing with the technical and scientific experts names and verifications. If some dude on the phone only wished to blab about it all, he's only selling you the product, not proving or providing anything except hot-air.
I come from a family that honestly believes anything running on fuel runs better or can be made to go longer by just adding Marvel Mystery oil...
And oh what a Mystery I have seen...
2008 Polaris Rzr 800
Elka custom shocks
Few other goddies