IRS quads have their advantages in the smooth ride regard in uneven terrain, and some extra ground clearance. The extra clearance really isn't as much as you would think though over your SRA machine. When an IRS equipped machines rear suspension is compressed it loses ground clearance, so that magic 10" measurement they list on their specifications list disappears some the minute you sit on the quad. Whereas, an SRA quads ground clearance is always the same,(unless you have a flat tire)
You have oversize tires on your atv by your signature, and that gives you in the 8.5" of ground clearance area, which IMO probably isn't much different than a loaded IRS machine. You also have much better towing ability than an IRS machine being a solid swing arm design, and better side hilling stability as well as being easier to get the rear end sideways without the I'm gonna high side feeling, and less parts to break and maintain. That being said the IRS quads are a nice smooth ride, and at my age and back condition I wouldn't mind one for those reason's. The power steering option would get my vote before the IRS though, as long as my SRA equipped machine had quality reservoir equipped adjustable shocks.
I've read about, but never ridden one before, that the Rincon IRS is the most stable atv in the business, although I'm not sure how they stack up against that simpler trailing arm IRS design by Bombardier, or Can am as they are now known.
I would save my money towards other good upgrades to your current ride if it were me. Good aftermarket shocks would be at the top of the list to give you a top notch ride,,you would be amazed at what some quality suspension parts can do to your ride. That, and until the IRS equipped 420 comes out with a manual shift version, or at least a ES edition to go along with the AT version I wouldn't buy one personally.
05 Suzuki DR650, Mikuni TM40 flatslide pumper carb,JE 10.5:1 piston,stage 2#190 Webcam,open airbox, Twin Air,full FMF system,Pingel fuel valve,Ricor Racing rear shock, Ricor Racing fork Intiminators, Progressive springs, Sargeant seat,DRZ250 tailight,custom plate,LED's,GPS,sumo fender,PT bars,Cycra brushguards IMS lowered pegs, aluminum skid,bearing chain roller,Pirelli,tank bag(gone)
06 Zuk KQ700, Kenda Bearclaw HTR radials Warn RT25 w/ syn. line, 1.5mm clutch shims