I ran 8 paddle Skats 20x10-10 on mine this summer and it did just fine. They look a bit small, but performed just fine.
I'd suggest a 22 inch 8 paddle if you can get them.
The bike can easily handle a taller tire than the 20's. Plenty of power.
What are you using for rims? I layed out and drilled a pair of Honda 110 rims for the larger bolt pattern. Worked just fine.
PRM Desert II bumper and PRM Control Grab bar, Houser anti-vibe Pro-Bounce nerfs, DS450XC shock mod, ROX anti-vibe 2" riser, Tusk billet gas cap, more to come.....