The last run I was on I saw this guy with 31s and a rear locker get high-centered and tow-strapped off. Another guy with 33's and rear locker managed to scrape through ok.
I know as soon as I go 31s I am going to bite off more than I can chew, get high-centered and kick myself for not doing 33s. From what I've read, I think you can scrape and squeeze through the hardest trails in Southern California with 33s - this is on, for example, The "Sledge" and "Jack-hammer" Trails a bit east of the OC/San Diego area (as long as you are locked front and rear and have a winch)
But, of course a smart move to 33s means lift, axle swap, regear, new wheels, & drivetrain work. All that would easily run me $5,000+. I may have to be a bit more conservative and go 31s, something I can do for probably less than $1000 and just be selective with the trails (and/or borrow somebody elses Rubicon "King" and drive Sledgehammer with that instead
)