9 foot is way too wide. Ok for light snow up to maybe 3" but as soon as you have a load up front it will push you sideways.
If you plan to use a plow angled 6 with maybe 7 would be max.
Even 8' on a 3/4 ton 4 x 4 GMC Diesel was often a problem, especially in wet snows, and that is considered the ideal plow.
I would not suggest more than 6' on your tractor.
With a truck we plow fast and curl the snow off to the sides.It flies. With a tractor speed is really not an option as suspensions are just not there. You'd be asking for trouble.
Now big and wide straight push with big side ears (no angling) like in clearing big parking lots would be a different matter.
Your nine footer would be handy but you would need to add lots of weight for traction.