Not sure, that'd be a question for Adam. It should hold boost up top even better once I add the stiffer wastegate actuator spring, but I'm not sure what the safe RPM limit is for this engine.
One thing to also keep in mind is how stressful higher RPM shifting is on the transmission synchros. That in mind, coupled with the impressive mid range power of this turbo, I have no desire to spin the engine higher than 7,000.