im not a noob. I know for a fact that ppd does NOT vary by 30% across the same damm work units?
sorry, not here long enough then.
yes, given the multiplying affect of quick return bonus, differences in the compute nature of individual wu(#of atoms, forces) and the way different cards handle memory(while shaders is a large part, other architecture features do come into play)....
long story short, yes ppd have in the past and most likely will in the future vary by that much.

EDIT:
ps not saying that it ideal or intentional, just that it does happen.
I am well below my thermal limit before the gpu starts throttling
you have monitored the gpu activity and it stays at 100%...never cycling down?
possibility...but not likely.