The Buick Motorsports book says that with proper valvetrain components, the practical limit for engines with titanium valves is 8500 RPM and 7500 RPM with steel valves.
Upwards of 9K plus for a few of these guys. This is using the latest T&D roller equipment w/PSI springs and Isky Rev Kits w/ 3/8" PRs and with an increased sense of doom.
With current parts available the N/A Stage II's are well over 9000. Mine is shifted at 8800 and thru the lights at 9400. Proper maintainence, clearences and oil control are critical to engine life. These small displacement non turbo motors need RPM to go fast.