31x11.5 or 32x11.5? advice?

Im going with the 2 inch suspension lift and possible a 1 inch body lift only if too much hacking is needed, i expect some and am cool with that.
I frequently run in sand so I think I want a wider tire. Plus they look groovy.
I had settled on the Kuhmo Mud tires in 31x11.5 as it seemed that would work great with my 3.73 gears but I noticed alot of 32 inch tires are only 31.4 inches tall anyway. Since they are only slightly bigger, should I just go with the smallest 32s I can find? It would open up my tire brand choices considerably and shouldnt perform too much differently, power milage wise that the wide 31. Especially since I could get an A/T for the highway, or is an MT better in sand? will do some easy trails too.
As a note, i can fit toyo 31s with no lift and no rubbing but I think they are a partically small 31.
Its a 91 explorer. I will use 15x8 rims either way, is it standard backspacing I want or Medium?

Thanks

 

[Eurobro]

Sorry to hi-jack thread but, will exhaust help out a decent amount with power issue? I already have the drop in filter with swiss cheese air box and am curious about if exhaust is worth my time. I want quietest exhaust and pretty much run no pipes after the muffler for the dump effect.