The TG84 should work just fine with your tractor. The only time you could notice strain would be with new/difficult ground that hasn't been plowed or torn up prior to tilling.
I had a 6' tiller on my 40 horse and I didnt strain the tractor one bit,so I'm positive you will have no trouble with the 84" frankly that's what i would have bought if it was available at the time.
Brian
Go for it! You won't have any problems w/ the 84" KKII! You'll be getting a great unit!! I use a 72" and its awesome!!!!
Post some action pics, pls...:dance1: