I have shimano xt's and think they are the best, but I don't have any REALLY technical stuff to ride on.
I would be nervous about crawling over rocks or roots at 1mph (especially with a 6' drop off on either side) and have to put a foot down quick, especially if you have your weight on it. But I guess some people can do it.
I broke two sets of xt pedals in the span of one year.
For clipless pedals on the mtb, I am having luck with PDM540's.