I've been running 31" STT's for over a year now and I don't have any major complaints. They have over 25000Km. on them and they're still around 75% tread depth. At 20 lbs. pressure they ride really good. As far as off-road use, most of my experience is in mud and they do really good in it.
Ive run the 30x9.5s on my CJ for years as well on a old Blazer. The wear and ride is good Ive been told theyre loud but its a mud tire. I found the price right good road manners never did me wrong on snow and ice nice trail tire. I also found the 30x9.50 not big enough in a tidal pool at a river bed at lowtide. http://akpostal.com/LBmud04.jpg http://akpostal.com/LBmud08.jpg
I'm running some 29" Cooper Stt's. Thse tires are great! They work well in the mud, very well in the rocks and seem to me pretty strong too. Also, they wear really well and there cheaper than BFG mud terrains. I would highly recommend them, I use them on my Daily Driver.
I ran them on my old 84 Toy for 2 years and loved them. They were great off-road and just fine on-road. I put about 25k on them and they were just beginning to show wear. The only thing you give up is sidewall strength, They are 2-ply where I think BFG and SS are 3-ply. I was going to buy a set for my 87 zuk when the dealer told me about the Courser MT or OTD. The Courser OTD is identical to the Discoverer STT and Courser MT is similar but not identical. They are made by Mastercraft which is a division of Cooper. They cost less so I bought some and couldn't be happier. If you are buying from a Cooper dealer then this might save you some, just a thought