As the title says I took the new GX550 and upgraded this morning... no rubs and it drives well. I don't think a larger tire would have fit without scrubbing, at full lock I couldn't get a finger between wheel and wheel well.
Wheels: KMC 18x9 18mm offset
Tires: Toyo Open Country 275/70/18
Wheels: KMC 18x9 18mm offset
Tires: Toyo Open Country 275/70/18