Basic Magnum question: Safe maximum RPM on stock internals?

My stock 300hp crate ran out of breath at 5K.
I ported the heads, swapped the M1 dual plane for a Pro Comp airgap, stuck a [email protected] roller cam in and the motor pulls to around 6500.
I run a 6400 chip in an old MSD 6AL box and hit the limit quite a lot on the 2-3 shift. 150+ runs and no issues.