Interesting. As the owner of an '08 F-450 with a 6.4 in it, this is good to know.
Every time I mention this truck to a mechanic they say, "Sell it!", but not to them.
Yes, I know the engine is as fragile as glass and it goes through oil changes twice as often as it should due to "making oil".
I had thought about trading it in only because it's an XL and lacks a lot of creature comforts. I even had to add cruise control to it. But it has only 90K miles and its only used as a tow vehicle for our 5th wheel. If I get 200K out of it I'll be happy. It looks and runs good, but has been hobbled by its emission controls.
The 6.4L Powerstroke (also made by International) has one very good thing about it - the high pressure Siemens K16 fuel pump. The current Ford 6.7L has used the Bosch CP4.2 high pressure fuel pump since it came out in 2011, and that pump has a poor reputation for reliability. The older 6.0L didn't use a high pressure fuel pump. The Siemens pump can push a lot of fuel, and holds up seemingly well. Otherwise, the 6.4L engine is not actually as robust as the earlier 6.0L in terms of internals, and the emissions system is a disaster (not one, but 2 EGR coolers, one hard to get to), the DPF system that can shoot fire out the tailpipe, etc. When these engines are running good, they are nice to drive. They make plenty of power and sound good.
We rent out part of the shop to a paving company, and they had a 2009 F-350 6.4L truck used for towing. They got 300k out of it and traded it, still running fine, with few problems...but they deleted the DPF and EGR system early in the truck's life. Of course now with the EPA cracking down on everyone for everything now, delete kits are hard to find and there are hefty fines if you are caught with one on your truck.