Well I've been browsing the forum daily since discovering it a couple weeks ago and have yet to post. I figured nows the time with a funny co-incidence, having to do with the book you guys are referring to. I actually shot the cover photo for that book, along with a bunch of the content photos inside the book. Eric is a guy that I met through a local jeep/4x4 forum years ago. It's funny to hear people all around the country/world referring to it. Pretty cool!
Now back to the topic. I have a 2" lift on my XJ and I'm running BFG's in 245/75r16's on Moab wheels. They're pretty close in size to 31x10.5 but slightly narrower. I get no rubbing on the control arms, although the back will rub the flares slightly when fully tucked. Keep in mind that the lower backspacing you get will give you clearance from the control arms, but in turn will cause you more issues with fender clearance.
For what it's worth, I'd stick with 30x9.5 unless you're getting a good deal on some used 31's or something(the reason I have the size I do). I'm actually looking to downsize in a few months when new tires are needed. That extra 1" of tire isn't going to do much for you.
-Jesse