The new Hemi uses hollow stem valves I believe, as does the 5.0 Ford motor for performance and high rpm stability in the valve train. If a guy wanted to take a hydraulic to the limit, there are a lot of things that can be improved, as mentioned. Beehive springs come stock on LS and New Hemis for that reason. Good (not cheap with the proper specs) valve springs are an absolute must. Titanium intakes, though expensive, would help a lot. Not going beyond needed weight in the pushrods, and finding nice light lifters all help.