you'll still be driving an oil burner down the trail...and they need to spool up
That's not entirely true.

Not all diesels have to "spool up." Only an engine equipped with an exhaust driven turbine will offer any turbo lag. Granted, diesels aren't the hottest deal going for mud racing or snow bombing, but when viewed in a rock crawling setting, diesels sure do make a lot of sense.

If you're spending a lot of time driving on the street, then turbo lag is a valid concern when thinking of engine choices. But for the low end torque that slow speed rock crawling uses, you're spending a lot of time in the 1000-1500 rpm range. A good diesel, turbo or non-turbo, will devlop all the the power you need in that power band without any assistance from the turbo, and thus eliminating turbo lag as a concern.

Highly biased,