I think that it depends on just what you mean by "off-road".

If you're doing real mountain biking, my experience is that you shift your position so much - both up and down and front to back - that you never stay in one spot for long enough for it to feel uncomfortable. If you do a lot of water crossings, I'd think that a Brooks might take a lot more care and maintenance.

If, on the other hand, you essentially ride your mountain bike like a road bike and sit in one position for extended periods of time, go with the saddle that you know works for you.