I bought my Banshee used and it had Holeshots(20-11-9s). Im still running them. They handle good, they corner good, they do okay in the sand too(which is where most of my riding is done). Ive never used the stock rear tires. The only other rear tires ive used are paddles, but that wouldn't apply to your riding.
As for the 22s in the rear, i say go for it, as long as you change the gearing to compensate(smaller countershaft or larger rear sprocket). If you do the gearing math proportionate, it should be very comparable, if not the same as stock. One tooth up front is like 2-3 in back. Ive thought of doing 22" rear holeshots and 23" front holeshots for more clearance when i ride in AZ.
For low end torque, i hear the way to go is the 2-1 Motofast exhaust, CV single carb set up, FMF ram valves, and boost bottle.
I tell you what pipes NOT to get for low end.....FMF Fatty Torque Plus. I just got those and it reduced my low end, but increased mid range and top end.
I currently run ported cylinders, .020"pistons, milled head rechambered for 92 octane, FMF FAtties, clamp on KN filters, 380 main [email protected]
level. I just installed a boost bottle yesterday, but havent ridden it yet. Future plans include FMF ram valves for more low end.