The problem you will run into running 18x10's is you will only be able to run a 30 series tire with something that wide or your tire diameter will be too big for the fenderwells, You'll get a tire that looks like a rubberband. If you want the look of a bigger tire in the rear, run 17x10's and then run 40 series tires.
all i siad is i was thinking about it. i have 17x8s all around right now but i want something in the back that will get me better traction, but i cant find any 17x10s. i would love get them if i could find the same rims but front one 17x8 and rear 17x10