I agree with the 31's on a spoa, for a DD and stock gearing, mine has 33" boggers and a 6 to1 t-case and tops out |removethispart|@ 55 and mpg are around 14 to 18. :
Heavy tires take alot of power, so be realistic on how much wheelin you will do and choose your tire from there!! A stock sami with some lockers can out wheel alot of built rigs!