I was in your shoes about 2-3 weeks ago. I was pretty much set on selling the Z at the end of the summer and saving for a down on a 2015 GTR. Then I went to ZDayZ and saw the Fast Intentions TT running at the airstrip event. IIRC, the car was putting down ~490whp at 7.5psi on pump gas (91). It was consistently running with a modded GTR (mid-pipe and tune) up to 140mph. The FI team was confident the car would've pulled on it at higher boost.
At $10k plus labor and supporting mods, it's a better move for me financially at this point. Plus, I just think my Z is too damn sexy to get rid of.
Here's the video of it hanging at 140mph with the GTR..