[rcweingart]

You also have to consider your cam, valve springs and valve train. Solid lifters run higher than hydraulic. Stiffer springs/double springs with more load on the seat enable higher rpm before float. Roller cams have higher ramp acceleration and required stiffer springs. Lighter weight valve train components, ie, rockers, push rods, retainers, enable higher rpm before vale float. All things equal, 6500 rpm is not unreasonable but the longer you run at that rpm, the greater the chance of breakage.