I put my RTV1100 through it's first "hard" run a few weeks ago. The group of guys who go riding at my property had things all set to go on a Saturday when the high was going to be 5 degrees. I took my daughter with me and ran it rather hard through the trails for the first time. I ran it so hard that I unseated the right front tire from the rim with 22 psi in the tire. I had a tank in my toolbox in the back of the RTV with 150 psi in it and, after wiping the rim and tire clean, was able to re-seat the tire no problem.
Some observations; climate control is great. I've run in 100 + degree days but that was the first really cold day. It takes the rough trails better than I thought for what is basically a 2000 pound ATV. Somehow lost my rear hitch even with the pin in it. I guess I ran it pretty hard. It will
not climb hills that the ATV's will climb. My Yamaha Rhino would climb hills that the ATV's couldn't make it up. It would be nice to be able to switch between low, medium and high range without stopping. The RTV1100 seems to be immune from the shifting problems that I had with the RTV900. As long as I stopped, changing gears was no problem at all. I'd shell out the bucks for a turbo for more power, but it just doesn't make nearly enough to justify the cost. Maybe a hybrid twin turbo setup? I think the tranny and axles can handle it. I literally bounced the living crap outta the 1100 on bumpy trails without bending anything nor breaking any steering knuckles or U joints or gears.
I've played with diesel pickups for years and I've posted my F350 4X4 crew cab dually that weighed in at 8170 pounds. Here is the run and the time sheet
YouTube - F350 4X4 crew cab dually 6.0 PSD 8170 pounds running 1/4 mile running the 1/4 in 14.24 seconds. Staying with a diesel, I think I'd need to go with a bit of a bigger Kubota displacement wise, custom injectors, custom injection pump, twins and a few other little tricks and I can see the RTV1100 keeping up with any side by side power wise. The next issue would be suspension, but that's another whole issue. I guess it depends on what you want to do.

I didn't run my F350 in full race setup trying to take care to the tranny. With just a little tuning only and hitting the tree a bit harder I broke into the 13 second bracket. To put that in prospective, I completely embarrassed both a 'hot rod' new Mustang as well as one of the new Camaros.
