According to what I've been told by some of the engine guys at Childress, on the new Gen IV SBC (NASCAR), they use a very low profile cam, flat tappet lifters and 1.9 rockers, combined with about 185# of seat pressure . . They won't say what the actual seat pressure is, nor the cam they run (Manhattan Project) but they're getting 9200+ rpm out of them for 500+ miles, WFO . .
Something to experiment with, perhaps?