since you put 17 as the latest you will go i will tell ya i do not regret the 17MC I purchased new and still ride with the others newer machines. yes the zuki is not as snappy off the line but top end is still compareable. if not there are plenty of mods you can do reliably. suspension is still better than polaris pro imo (not khaos) and pogo doo front ends. 17s had a great shock/valving package if you get a MC or limited. Get a MC tho. It has most of the newer chassis mods the current cats do. clutches do not explode in fact i think they offer better belt life than polaris ta boot. cheaper belts that last longer. a 17 axys is not a bad choice at all, I just like the robustness of the cat. A-arms dont bend as easy and motor goes at least twice as long before needing rebuilt. Either brand will need clutches thoroughly gone through if its higher miles.
Going forward if you have a MC, you can literally bolt on anything you like better about the newer cats. just a matter of how deep your pockets are. Im not sure you can bolt an 850 into an older axys or their newer plastics, but polaris has TONS of aftermarket options anyway.
I wouldnt buy a doo 850 older than 19 unless its a KILLER deal. first two if not 3? years of the 850 doo were belt exploders and them things aint cheap. seems like they are the most expensive sled on snow to operate is their main drag to me, I actually like the handling fine. kinda fun. Ive never tried to hang long sidehills on one though. I know they dont walk across set up snow easily like a polaris or twin rail cat can.