It has been my understanding that as long as you are accelerating, then you should not shift gears. We are limited by the engine blowing up or hitting the rev limiter, but taking it to or just past redline would probably be ideal.
If the gearing multiplies torque, would you not accelerate faster in a lower gear than in a higher? Therefore, less engine torque in a lower gear will accelerate you faster than more engine torque in a higher gear? There are trade offs, but generally speaking between shifting at 5500k or 6500k.
