i do a LOt of wheeling and in my own personal experience i have gone wheeling with a lot of guys running 10.5x33 tires verse my 12.5x33s and i have always had better traction and performance than any of the skinny tire guys. all trucks are set up very similar, most are body lifts with open diffs (me) or l/s rear. from what i have experienced the wider tires always work better in any situation. better floatation and grip in sand and snow, dig and push harder in the mud and grip better on the rocks. one advantage to the wider tires off road is the increased traction making it harder to break the tires free... this is a common problem with skinny tires. they break traction, start to dig a hole, then they are stuck.
this is just my opinion based on my experiences
2005 DSG ranger 4x4, 4.0L 5spd.
Dual magnaflow exhaust, 6000k HIDs, kenwood deck with 2 10" alpine subs
33x12.5 wrangler mt/r kevlars on 15x8 ultra nomads, shackles and cranked t-bars!!