I've had my xj on a set of 31" falkens for about two months now, with maybe 2k miles on em.
So far they've been fairly quiet on the freeway, and the heep hasn't had too many issues driving around with em on 3.55's.
They kinda wander a little bit on the freeway, more than the old goodyear wranglers that were on it before.
I think that is caused by a few issues, mostly related to my jeep:
1) my control arm bushings are shot
2) stock short arms on 3.5" of lift
3) my steering box being on its way out
4) I don't have great contact with the outer edges of the tread pattern to the road surface. I'm sure thats caused by having the tires on my stock rims and running slightly too high air pressure. (30psi)
I like them so far, although I cannot comment on how durable they are in rocks long term... They did ok when I went and was fooling around in Holister a couple of weeks ago. did allright messing around on the rocks at the quarry. I really like that they're quiet on the freeway. If I keep my foot out of the gas they seem to get ok millage on the freeway. But I have not had the time to do a long highway road trip on them yet.
Anyways, I hope this helps.