I drive the 2.5. Honestly, I've had really good luck with it. DO I want more power, yes... Do I need more power, almost never. I've been wheeling for about 9 year on my jeep and can count on 1 hand the number of times obstacle failure was due to the motor. Part of that is the way I wheel and part is the terrain I wheel on. Having said that I think many obstacles would have been easier with a bigger motor but in general I'd be willing to put my 2.5 up against a 4.0 anyday.
If you're considering the 2.5 for gas mileage, don't bother. I'm getting the same or shittier gas mileage than my 4.0 friends.