Thanks man.
I know people that own both, and the 3.5 blows away the 5.0, everywhere.
Torque, towing, mpg.
The only thing the 5.0 has is a loud V8 growl, if you like that. I think the V8 sounds awesome too...in a Mustang. Personally, I don't want a loud truck.
The 3.5 is very quiet, but when you stomp it, it has a little growl of it's only, and it really sounds like a V8, seriously. That only lasts for a couple seconds, then the exhaust goes quiet, you here a faint whistle from the turbos for 2-3 seconds, then everything gets quiet again. By this time you should be amazed that a 7000lb brick is moving so fast.
Tell him to drive both before he buys, or all 3.
The 2.7 ecoboost is supposed to be very strong also, and with the best mpg, but I don't know anyone that has one.
2.7 ecooboost V6
325hp 375 trq
5.0 V8
385 hp 385 trq
real world mpg 12-13 city, 18-21 highway
3.5 ecoboost V6
375hp 470 trq
real world mpg 18-19 city, 23-26 highway
Of course mpg varies by fuel, elavation, driving habits, etc.
But this is what I found and saw personally before buying