ok my 2 cents here, a 25 gallon sprayer is going to be a LOT of weight on the ATV, odds are your going to notice this right off, and with that a solid rear axle will handle it better, but you still might need some better shocks to help it out!
so that kills the IRS iea right off IMO
NEXT , I don't think there will be a BEST model for you, all the older one's had pro's and cons, as do new one's
ONLY new you know aht your getting, used, your buying into a gamble of IF it was cared for, NOT abused and so on!
SO< if you have the coin, go NEW, unless you really really KLNOW the seller and they are NOT lying to you
countless treads on here and else where about folks buying used and finding all sorts of MAJOR issues, and there GOOD deal went south super fast
Unless your the type of guy that doesn;t mind FIXING things
GO NE and go Foreman!
them Rincons, are NOT made for work, there trail rides
the Rubicon is NICE but the foreman will still be more of the work tool atv IMO and this is what happens to atv;s on ranches and farms, there tools more than toys!
as they say right tool for the job !
if your running a HAND wand sprayer, Power steering will be a BIG help and worth the costs in the long run if you spray a lot while driving!
so food for thought for you!