Right now it's the 37's and 40's that are difficult to get. I almost went with the 285's on my truck but after 270's tires get super heavy. 50 - 75lbs heavier for a set of all terrain. After having to add negative offset to clear I deemed it a no go to prevent big repair bills down the road...
IMO, that size tire you have mounted on the back is the holy grail of perfection for sizing on the GX or any off road rig short of a rock crawler. With a modest lift, sizing up to a 31.5" or 32" will get you anywhere you need to go. Add in weight that is equal or not much more than stock, no...