This is highly debatable and you know it!!! All depends on how many miles he puts on the truck per year. The less he drives it, the longer it takes to break even with the cost for E4OD swap. $5k is a lot of money do dump all at once into something like that, if he's using the thing to make money like you do with yours then yes I could definitely see some merit to it, but if he's not then IMHO there are much better ways to spend that kinda cash.
Want some numbers, I got 'em for ya: we went from a 4-speed to a ZF last year, cost us like 200 for the trans and another 100 for clutch (practically brand new junkyard score) and oil, so about 300 total. Fuel economy improved by 2mpg IIRC, from 13 to 15. Assuming $3 per gallon that means cost per mile dropped from $0.23 to $0.20, so the savings were $0.03 per mile. It therefore would take us 10k miles to recoup what we put into the ZF swap. Now in our case we're talking <$500 so not that big of a deal overall, in his case we're talking 10 times as much initial "investment". Care to calculate how long it will take him to see a return there, not even profit, just return? Assume his C6 makes for fuel consumption as lousy as our truck with the 4-speed, and use your own average numbers for the E4OD. Ignore his GV for worst case scenario.