You also have to consider shift time, if you're 6MT. If reducing the RPM you shift at in every gear causes you to have to use an extra gear, it's not worth it.
For example, in my LS1 RX7, if I shift at redline in every gear, I can go through the traps just at the very top of 4th gear. If I shift a little earlier to take advantage of a handful more torque, I have to shift to 5th gear at the end.
The few ft/lbs of torque does not make up for the .1-.2s it takes to shift from 4th to 5th - I've tested it.
Sorry if this does not apply to N54/6MT, the gear ratios may allow more in that example, but it may be a worthwhile point for people thinking about upgrading to a higher ratio M3 rear end, or similar (My RX7 has a 4.10).