You'll be fine with the 10.5 Ags. Everyone has an opinion including me, what works for some might work better for others, or not.
I do most of my plowing at a plow day even where I'm following some sort of furrow left behind by the plowing person in front of me. half the time its not much of a furrow, the other half its to deep.... Sure an 8.5" works better at times but seriously the difference is not that noticeable with our Cub Cadets. If you have 8.5s or 6" Ags in soft ground while plowing you could spin half a tire and be stuck/hung up before you blink whereas a wider tire might get you through a soft area.
After install your Ags you'll be happy - that's my money back guarantee
