With all of the scarifiers down the 84" might be too much, however, you don't have to put all of them down. You could use five out of seven, or whatever works. But you still have the full 84" when you are grading. Either one would work for your tractor, I think I might go for the bigger one for the added versatility.
I've used mine with only three scarifiers down on some tough stuff, just made a few more passes. Having the wider blade was nice for the finishing work after everthing was broken up and I just had to level the road up. Takes a bit of practice, but really came out nice.
Really tough stuff, I use the two bottom plow on the big tractor, and the Kubota follows up with the box to break up the chunks and level off. Then a few passes with the york rake, and it looks new.
Jerry