A 1,000 RPM bump is non trivial. Traditional weak spots are piston rings and the valve train. The trade-off on piston rings is thick/heavy for long life, thin/light for high RPM's. I suspect the rocker/followers/hydraulic lash adjusters are limiters on these engines, based on the change to direct bucket followers on the heads in the Jags (according to T. Haines).
Spinning an engine faster is a classic way to get bigger HP numbers, but creates problems with normal driving. If you want a car to feel fast: push down on gas, have car lunge forward; you want more torque. High reving, peaky engines are better suited for track use.
