As with ANY used vehicle, YRMV ....I can't influence your decision in any way.

The 7.3 will be in a truck from at least 2003 or earlier... (the WHOLE truck will be at least 8 or more yrs old)
the 6.0 will be in a truck from at least 2005 - last time they made them.

As my signature states, I've had 3 of them...
and while my results are not statistically relevant, neither is the one case sited in the post above.

In MY case, the 7.3 was the worst of my bunch... Ford bought it back within a year,
the 03 was traded in on the 05 because I like the Ex so much that I wanted the last of the breed,
now my 6.oh has 119k HARD miles and I still love it !

I am perfectly comfortable sending my wife off on an emergency trip to Memphis in it this week.
I wanted her to fly, but she said she would rather go in the Ex. Fill it up before she leaves and she doesn't have to stop for fuel until after she runs around Cordova and Germantown for a week !!!

It is the BEST traveling vehicle I've ever had, and I had 2 motorhomes ....

I like mine so much that even though the wife's car is newer than mine,
she gets a new one this year and I'll pass on my turn to get a new one !!! Is it perfect ? No, but it's as close to it as a used vehicle can be IMHO...

Good luck on your decision, and my guess?
you'll have bashing and "mine's better than your's" for 100's of posts....