Back to your shifting point.
Remember This!
If it kicks you in the pants when you shifted(you are over revving the eng).
now for the explanation. if you run it past its power potential (RPM) the eng will start to nose over(slow in acceleration) and When you shift it will kick you in the pants. If you shift it on time it will continue the exceleration threw the next gear.
I bet you you will mph and et at shifting at 5500esh. I really don't think there is any power left at 6000+ rpm. It may sound cool but it will be faster shifting sooner. You have got use to the long song at 6500 and it will be tough to shift it sooner....but it will be faster.
