Here's my 2 pennies.
I LOVE my 7.3. BUT I get about 14mpg. I would love a 6.0 if it was a 6 spd. Heard tomany people splitting there torque shift cases. That is just what I have HEARD. Don't jump my nuts, not claiming fact or fiction.
6.4's I think they look awsome, I would just waite a year or 2 more to let them work out the bugs.