I've been down this road before. If you got the itch really bad, maybe you should consider selling the Z and starting over with a different car that has more power potential.
Yes you can squeeze a few more ponies without going FI, but if you're not going to go down that road and you really want more power, the Z platform is not going to get you there.
Think about what you really want to accomplish. If you don't want to change to another platform, your only other realistic option for a lot more power is to go FI.
Best wishes with whatever you choose!
