The ATP turbos are fantastic! I would think since you have other customers, BPD, Steve and others with upgraded turbos making considerably more power on their dailies you could do his as well.
Is it the 2013 year difference aka lack of fuel or something else that has shifted your safety point down from 440ish to 400?
I'm working with Steve now on the fuel system and other items to get some more umph out of it. I completely disagree with LMS feelings on the 450+ HP barrier but then again I'm the only one who's been there besides the truck with upgraded turbos and fuel system I worked with. He's still running fine as well. ATP's truck is still running great also from my understanding. The empirical evidence seems to point to the fact that 450+ so far isn't an issue, detonation is for sure. There has been some rod failures but when you produce this many engines you will have a percentage of "bad" rods from the factory no matter what you do, byproduct of mass production. Those rods are failing at stock or near stock HP levels.
Time will tell as more people buy these vehicles and do more to them. I hope for everyone's sake 450HP isn't the wall for reliability.