I owned an 03 and 05 4Runner with the V8 and currently own an 06 Tundra with the same 4.7L V8 in it. That motor is bulletproof....never seen one in for engine work or major repairs. Same goes for transmission and 4wd system....all great stuff in there.
The V8's do have a timing belt with an interval on it, so it's good to check if that has been done. It is a non-interferance motor to the best of my memory, so not the end of the world, but one of the larger maintenance items.
Expect ~2mpg loss over the V6. The V8 is an iron block, so very quiet and smooth running. The V6 is a slightly newer motor, the remote oil filter is nice, although it makes a little more racket being all aluminum. V8 has more low-end....in a flat out unloaded drag race they are very close. V8 has the edge in towing as you would expect. The V8 has a slightly heavier steering effort with more weight on the front end.
Keep in mind that the V6's can be put into 2wd, whereas the V8's have a full-time 4wd system. The full-time works very well with no binding whatsoever.
You honestly can't go wrong either way, I would flip a coin on the motors and be happy with either. The V8's got a power increase via added variable valve timing in 2005 and newer. Any other questions ask away....I have a lot of useless 4Runner info in my head lol
