For me, its the pro stock Hemi's...Seems like if you were to raise the cubes up and put the heads on a +600 cube motor and brought the power band down into a more usable range, it would be the best of both worlds.

I think a guy on here has one on a billet block 650 at cubes running very low 7's or better normally aspirated...

For an all out motor, that is probably what I would run $$$$

The P5 I believe was the predecessor to the Hemi 99 design.