Hmmm, the stock rev limit is 6250. 6800, are you running a standalone, or a reflashed ECU, otherwise I call BS, Nissan must have given you a faulty tach.
Yes, the stock rev limiter starts at 6.2 or 6.3 but it doesnt mean that its gonna stop there and not let u go down more. You can also rev it EASY at 6.5-6.6. Just got to kno how to drive u car man