Going from a BFG AT in 32x10.5 to an MT/R in 32.11.5 didn't really make that much difference in gas milage for me. They are louder, but not too loud either.

One thing that I did notice was that the tuck wandes a bit more with the MT/Rs as I expected, since the MT/R is a more agressive tire than the AT KO, thus road manners might not be as good.