I am running 19's here in slc (I only ride the dunes) I run a 50/50 mix of race gas. I think with 20's you would be safe to run premium pump gas. But why run the 20's when you can run the 19's? Run the race gas, get more compression, its the shiznitt!!
Oilsmoke, and JJfizzle, lets plan a bansheehq dune trip to sand mountain I'll drag with guys!!