Found this article talking about regens
Johnson Matthey Catalysts - Emission Control Technologies Filter Regeneration

Looks like the optimum temperature in the DPF for NOx based regens is 250-350C and O2 based regens are up at 550C+.

Basically, if we can run the truck with sustained DPF temperatures above 250C(480F) we'll benefit from passive regens

The problem with our engines is EGR is used to minimize NO before leaving the engine so there's not much NO2 after the DOC for burning soot at 'low temperatures'.

My DPF temperature normally runs between 350-400F around town. I barely touch 500F on long freeway shots lightly loaded

 

I agree. Higher EGT's for passive regens like the 6.7 would help greatly.

6.7 uses the urea to keep the NOx down.

Higher temps in the dpf while towing is why I can still go up to 130 miles between the regens.