Well it depends. If your looking to stay near stock height, I wouldn't suggest going with a tire size larger than 275 and a rim size no bigger than 19. At that point, everything should be flush with a little tire tuck. Also look at the offset sizes on the rims, because that also makes a difference with clearance in the wheel well.
I'm currently running 18x8 upfront and 18x9 in the rear with 235 upfront and 275 in the rear. I'm +20 in the front and +40 in the back. And I'm still on the stock suspension. I've only got maybe 1/4" gap between the tire and the fenders without a roll and it looks pretty good.