I am far from an expert, but have done a little research on the matter as I am also in the process up upgrading wheels/tires. This is what I have heard from numerous sources: with a 2" leveling kit, you can run most 35x12.5 tires on OEM wheels OK. Without it, you should be able to mount 33-34" tires less about 12" wide on OEM wheels.
As far as the Rugged Trails go, they came stock on my truck and I haven't been very impressed. Ride is nice and soft, but handling, slippage and mileage haven't been that great. If you only drive around town and stuff and don't do any off-road or hauling, they are fine, but I would recommend a nice LT or A/T tire. Besides, it might be hard to find a tire in that size range that isn't an A/T or M/T tire.
Hope this helps