Your fine with an all terrain type tyre upto a 26", anything above 26 and you'll need a gear reduction. If you go super aggressive with a 26" such as outlaws I personally would consider sticking with 8 or 9" width all round to help minimise power loss.
This is with 26 Zillas. Still has Plenty of clearance with these on. I don't know how Swamp Fox's compare in weight, but I'd stick to a light tire. I find when I get in heavier mud or something that I keep it in ESP mode to hold it in gear and keep my revs up, but I found myself doing that even with the stock tires on.