mine used to do this, i put a 4AGE in and the problem went away.
what do you mean it revs to 6,500 RPM on high octane and 5500 on 91 RON, 4ACs have no power anywhere, l;et alone above 6,000 RPM.
to answer you question without a search, you can make the 4AC a bit better, but you would be better off spending the money on ANYTHING else, as the motor has limited potential.