Rule of thumb I've heard and go by is shift 10% higher than peak HP (5900-6000) I would redline it around 6400 unless your valve train isn't up for it (hydraulic?)... Try adjusting your shift point in 100rpm increments and let your time slip tell you where you want to be... better to err on the short side especially for 1-2 shift for best ET.

Better than the rule of thumb: where does it stop pulling?

-Chris