Aye, I have a set of extreme trekkers. Nightmare on the road, noisy like you wouldn't believe, handling interesting.
Off road they are brilliant in the mud but not too great on rocks - too much of an open tread.
Wear - expect less than 10,000 miles
Personally, when mine wear out I think I'll replace them with a set of 255x85x16 BFG MT's. I just don't think we have the terrain that suits them. Rainforest yes - but not here.
HTH
Dom