The only thing that will matter is what and where you are plowing. If res. go 8' 8.5' will be a little bigger and tougher to manuver (depending on the sizes of the driveways). My boss uses 8 footers on everything from gmc 2500- ford F-450. He plows lots and it really doesnt affect it in my opinion. The tires might tread a little in the snow but not that much where it will affecct your producticity. If your doing lots just go for the 8.5.
I also put a 8' Fisher on my 2500hd, all my other plows are 9'+ so I wanted one that I could cleanup between cars and other tight places but if I wanted to I would have put the larger plow on, you would not believe the amount of difference that only 6" makes. Just my two cents
I have a 01 2500 HD Western 8.5 MVP... Great plow, no problems with single wide drives arround here. The V is great for getting arround tight corners as you have the option to expand one wing at a time.
Only thing with this truck you will want to crank up the torsion bars a few turns as thay all seem to come at their lowest setting, Causing quite a bit of front end bounce. It's something I'd ask for when buying the truck as you will need to get an alignment if kept cranked all year long, most likely dealer wont charge ya if it's when ya buy it.
Your truck can handle a variety of plows and having proper tire clearance is very important. The longer the truck (ext. cab, quad cab or dually ) all add to the problem due to increased turning radius.
The power plow lets you pick the size from 8' to 10' with the touch of a button from inside the cab. The wings pitch forward to make a scoop and with one forward and one out straight you can plow with little to no trail off to clean up.
Good luck with whatever plow you decide to go with.
It's good your happy with your current combo, however if you are plowing townhouses you should really check out a back blade for pulling the snow out of the driveway. It's a real time saver and balances the truck out. Jerre