I have the 39.5" IROK's and haven't driven them other than to and from the trails locally. So, they don't have many miles on them, nor do they show signs of wear.
I would say, since they are the same compound as most other swampers, and given the fact that they have larger voids, meaning more contact pressure on each tread they do have, would result in lesser tread life. This is speculation on my part though.
I talked to INTERCO and they are planning to release the 42" IROK in the first quarter of 2004. I am hoping to get a set of them for testing. I'll keep you posted. That's all I know about them other than they work great offroad here in the midwest. It should snow soon, so I'll test them in the snow as well. /forums/images/graemlins/thumb.gif