The other thing to consider, is the ground clearance, and the suspension travel.
I had a Kaw mule 610 (now called sx). It worked well. No problems with it, and would go pretty much anywhere. Speed was limited to 25 mph. Only issue was the suspension. After a day riding in it, you felt very tired. Had 3 inches suspension travel Up graded to a Polaris ranger 900XP, 2014. That won't fit in the bed of the truck, however, it felt like I was driving a Cadillac in the field and not tired at all after a days ride. Speed was limited to 65 mph. So, pull that on a trailer.
The pioneer 500 has 6 inches suspension travel and the Polaris 570 has 9 inches with a better ground clearance as well, so I would go for that machine (Polaris) based on the ride alone.
The Polaris 800 (I never owned one) main complaint that I heard was the position of the engine would tend to heat the cab area more than the later models (900 and 570), but I can't say that was that bad since I never experienced it myself.
Whatever you end up getting, at least get a lower half windshield. Keeps the wind off your face.
The full windshields alone tend to suck dirt back into the cab area, so if you go that route you might what to get a full cab.
2016 Colorado LT, Laser Blue,CC,4WD,2.8L diesel, ARE Topper