IIRC, the XTerra's 4.0 V6 put out similar HP and TQ numbers as the Toyota 4.0, although I felt the throttle response was better with the Nissan. I think it was a bit lighter too, so yeah, it did feel a bit more eager to get up and go than the 4Runner, but not by much. Seats in the XTerra were not good, IMO. I would not like them for anything longer than an hour, but that's my personal opinion.
I'm sure someone could pull up the exact specs (i'm too lazy to do it right now) but I believe the Xterra, in addition to being lighter than the 4runner, also had shorter gearing.
I drove the Xterra (6 speed) a little bit, and it definitely felt a little quicker than my 4runner, but then again it also gets horrible mpg. If I had to choose between the 2 options, I'll take slightly slower but better mpg any day of the week...I have no trouble getting 24 mpg on highway cruises (staying right around 65 mph).