I think either one is up to the task. After driving them both, I've got to say I enjoyed shifting through the gears and the extra power of the 5.7, fun, fun, fun ! I felt the extra cost over the 4.7 would be $$ well spent for my liking.
Having said that, we pull our 19' with a Tacoma comfortably. 6 cyl, 235 hp 4X4 with tow package. Just back from 8500 miles cross country, avg'd 12.5 mpg + with no issues. I had my doubts when the two of us left, but am assured now that we don't need a bigger truck. *( much to my dismay ! )
The Tundra is a BIG truck ! I think you have to determine realistically how much towing you'll be doing, and what other uses the truck will fulfill for you because those "other" miles will cost you dearly in fuel the rest of the time.
Good Luck and Happy Streamin' !!
