Hey Rajun,
Mike is right on the money about taller tires eating up horsepower. When I went to 25" tires on my Hustler, I had to gear it down 30% to get the machine to perform right.
IMO, Vampires are the best AATV tire out there, they will swim with V's facing forward, climb out of a muddy bank better than anything and mud with the best of them. HOWEVER; and this is also my opinion and worth about as much..I believe exerted psi is the most important factor in mud performance...even over ground clearance. Wider tires are what decreases your exerted psi, so if you found the widest 22" tires available, you would get the performance you are looking for without the horsepower loss and drivetrain stress. Vampire does make a 22x12.5-9 I believe, and I am sure there are other wide 22" tires out there.
The only two things you will gain are ground clearance and ride comfort with the taller tires, but it will cause other problems for you to deal with. If you were to have 22x12.5 tires vs. 25x12.5 tires in a bottomless mudhole, I don't think there would be a significant difference in performance since amphibs don't dig down to find the bottom like a quad, the goal is to stay on top....
I have MattO rims and run low pressure and really like them....great price too.
Hammers should have warning labels.