Sounds like the Arctic Cat will work fine. I wouldn't go too big on the tires. Try and stay reasonable. You don't want the machine to get too tippy or lose a lot of power with that 550. Radials are a great idea....especially the tougher ones with good sidewalls.
Relaibility should be about equal to a Polaris....didn't know about the axle thing though. The belt on those things are supposed to last a very long time and need very little upkeep. When you find one you intend on buying be sure to look up any recall/issues and have them addressed before you shell out your money.

 

if you do decide to go with the cat, ive read on here somewhere a guy had bought several arctic cat 400 trv for his buisness and had nothing but problems with them. but ive also read people that have never had a problem with them. The 500 cc or 550 seem to be pretty reliable though. ive had a 500 in the past and never had a problem,sold it with almost 5,000 miles on it. There is also another guy in the cat forum with 16,000 miles on his cat and i think it may be a trv.