Thx 08Datsun for the info on your 08.
The concept of "quenching" the tranny fluid appears to be right, since water is a better transfer medium than air. There has been some real number testing here:
http://www.thenewx.org/forum/showthread.php?t=30287 where ultimately the radiator-atf cooler is the most effective than just the atf cooler alone. They recommend that if you do the bypass, add a secondary atf cooler.
Again, i'm betting (hoping) that the Nissan engineers had fixed the problems on the 08+ Pathfinders. I have been searching on both the Xterra and Frontier forums to see if any late models have the problems and so far none.
I'm even more concern of the bypass since I have the V8 which puts out an additional 100lbs of torque, and when I off road and going <30mph, I want the best cooling possible.