Another good option is 285/75r17 which is a 34x
For a fact, just had the BFG M/T's 285/75R17's and with a BMC and lift, I had full lock-to-lock, and full compression at all 4 corners. They fit great!
The 315's (35") have now do rub just a wee bit and that's after tearing out the wheel well liners and pounding the pinch weld. Over the holidays I'm going to look into that a little more and see where it's rubbing and see if I can address it.
What is the reason for you to change from 285/75/R17 to 315/70/17? GX is not my daily ride, I have a company vehicle for that. But, I use it for long-distance road trips and occasionally camping on the weekend. I do plan to go on trails but not rock crawling..