Well, I'm not likely running too lean at 75% throttle and above. You should be most concerned if you're running lean at full throttle.
At part throttle the ECU corrects the mixture to 14.7/1 AFR; once you're outside of the range where it cannot compensate, it sets an engine code.

 

i think a dyno tune is in order for you my friend... if you butt is as talented as you say, then more power to you... but if not, you'll be thanking yourself for double checking.

 

Is the 'Knock Monitor' function supported for the Z?

 

yes