yea, Im going to go with General consensis. You do not need (nor would want to) change anything on the Z-tune, especially ecu. as it is already a mean mutha as it is. and has been extensively tested and tuned to what it is now.
Only reason to change ecu, (which would require retune), would be if you were going for more power!, and in that case thumbs up. But even saying that, whats been said already about the Z-tune, is that its already got Immense acceleration, so more power might not really be required.