Yes I went with with 4/4kg. Slightly softer in the back giving a little more grip. Generally speakingthe softer the suspension the more grip you will have but the less dynamically the car will respond to direction changes. I'm trying to set my car up for even grip front to rear and even handling. That's why I will running 235 wide tyres front and back rather than wider on the rear.
240z are around 48:52 weight distribution so should have about the same spring rates front to rear. Corner weighting should remove that slight imbalance. My car has a slightly heavier engine so should bring it to around 50:50.
With the recommended BC spring rates you would be front grip biased. Although with a 48:52 balance the rear would be notionally 40kg heavier on the rear for the standard curb weight of 1044kg so maybe the extra 1kg spring rate might be needed but it seems a big change to me.