Stick with a narrower wheel and tire for less weight. Run a 33x10.50 or 9.50 tire on a 6" or 7" rim. You can get used stock alloys in 15x7 for pretty cheap and they will probably be the lightest. I run the 33x10.50s on 15x6 steel rims and there was a world of difference compared to running 33x15.50 Swamper SXs (bias ply) on 15x10 steel rims. I would basically lose 1 gear on the road with the heavier tires.

One other advantage of the narrower tire is you can run them at higher pressures, the 9.50 and 10.50s are rated for 50 psi max, the 12.50 is only rated for 35 psi max.