I have to agree with the OP
In my Condo Building there are 3 G37's. When they drive away, there is a nice purrr to the exhaust, like the FX45 but the Z sounds really really quiet.
That always upset me, I figured the Z should sound much sportier of the 2
However, I have the FI exhaust now, so all is well and I don't feel inadequate with my exhaust note