The E4OD is a weak sister. I ran a small fleet of Powerstrokes (42 to be exact) and 75K is about all they are good for when towing any kind of trailer.
Some last a little longer, some a little less. We serviced them every 15K and all were equiped with large add on coolers.
The five speed is ok, it has weak second gear synchros.
The clutch is terrible though, any rough use and the heat wipes out the dual mass flywheel. This makes a clutch job expensive as hell (somewhere close to $900.00 for parts). I would not reuse a dual mass flywheel no matter how good it looked at clutch replacement time.
I think I would go with the automatic, it will work great throughout it's lifespan, when it fails have it rebuilt and install the latest upgrades (I was getting them done for $1200.00). The 5 speed never works very well, the 3-2 down shift is terrible even when new.
It's a shame that such a great engine and truck package is stuck with such poor transmission choices.
Good Luck making this decision!