You may never take the n54 Z back to the track, but I think you need just a couple tweaks and you will have a totally different perspective. I've seen your posts and I see we track at the same places....but never at the same events. Hopefully someday we can meet up.
I have a 2010 n54 e92 335i and a 2013 e92 M3. My n54 335i is equipped with meth injection and i'm able to run up to 19psi in the middle of summer at Willow, for example. Meth injection at a 50/50 mix is fantastic in keeping oil temps in check, particulaly in very hot conditions.
As an example, with just a DCI, catlezz dps, Procede and meth, on the back straight my car hauled down 600 and 700 HP cars at my last track session in June (one car was a heavily modded M6 and the other a tuned biturbo 63). My oil temps never hit 250. Top end pull is crazy. In fact I raced an ESS VT1 Supercharged M3 later in the day on the back-straight roll on and it was very close and in fact the M3 gained the early lead but I was pulling in the triple digits.
In addition to the four bolt on engine mods, I also have coils, LSD and Michelin Pilot SS tires. That's it.
I haven't experienced the M at the track yet but my guess is that my 335i with just these seven mods is more capable at a fast track like Big Willow. Sure the M3 is more precise, and the 335 is a white-knuckle experience in some corners but it has tons of grip and is a rocket at any speed and at any RPM. Now, mod the M3 and it will of course easily take the 335 at the track but that's expected.
Anyway if you have the budget for these mods, don't give up on your Z. It will surprise you.
Daily: 2013 e92 M3 MW FR DCT ZCP / ESS VT2 650 S/C, MRF mid/Akra slip, ST BBK
Track/Airstrip: 2011 997.2 Turbo S PDK / 501 AWHP & 536 AWTQ Bone stock on a Mustang dyno
Beater: 2013 X5 3.5sport