It is difficult to say.
Alot of people here I have read can rev their A14 engines to 7000rpm with stock bottom end.
A12 I have'nt read of alot of people doing the same. I think Nissan did something when they changed to A14 to make it more of a balanced engine.
I have the A12 GX motor.
I have driven it hard quite a few times but cannot get it over my heart to take it past 6000rpm.
Between 5500 and 6000rpm it starts to vibrate and make a hell of alot of noise.
The GX double valve springs makes a redline of I think 6800 to 7000rpm.
I will NEVER take it that far.
It would definately drop a rod or vibrate something loose.