Smokin Lariat

I've got a 06 Lariat XLT 4x4 running Foose 20"x 8.5" wheels (not sure about offset?) with Pirelli Scorpion 20s. When the time comes for new tires how big can i go on those wheels? Keep in mind I'm looking for a highway/street tire and I may be lowering the rear end 2" just to level up the truck.

I also don't want to deal with any rubbing or trimming of the lower valance.