What is a good combo for turning high rpm?

More head, more carb, and a solid roller. Maybe your rotating assembly in a 340 block, the bigger bore size will eliminate any valve shrouding problems that seem to pop up with the small bore motors. If you're gonna spin that fast, you should be making power at that rpm. If it's going to lay down after 6700, that extra 1300 is going to be a long way up the road.