Doesn't take much to get a Cat in the 420lbs range as it is. A buddy and I have three between us and we are in the 420-430lbs range for a running sled(least amount of fuel possible but still running)
Having snowchecked 3 sleds in 4 years, and two of those Polaris's......I actually like the old 800 Axys over the 850 Axys. Hence why its for sale and the older '17 is still on the truck. I also have a little bit of work done to the 800.
I personally am not a fan of the higher chassis that is the Matryx/Axys but love the stiffness of them. My Cat had rail issues(twin rail) but has been pretty solid since. Chaincase adjuster was upgraded before anything went wrong. Front skid shock got an upgraded axle before it left the showroom floor. Handlebars have been known to bend like Doo's. Fairly simple considering the 850 Axys spent half the year getting a new engine at 150 miles. then a couple ECU flashes....not worth my time to own in all honesty. And not better than my 800 for my type of riding when side by side.
My Cat isn't stock by any means now. Boards, skid, tank/seat, hood, steering, skis, etc etc but it's because I like the platform the best so I keep personalizing it to my liking. The 800 Axys is damn good with some shocks and a little bit more power, almost stock.
I just can't deal with the floppiness of the Doo. It's so wavy and flexible that I don't like it. Works great for new riders or riders who rely on sled skill versus personal skill(older, lighter, shorter people as well)
If I did have a Doo, I know exactly what I'd do to stiffen it up and make it more like a Pol or Cat. But I think I'm covered as it is, no need to fix a sled I don't want any part of anyways.