While my Kumho Ecsta XS tires aren't as sticky as yours, I too have added the GT3 brake ducts to my '99, and use either fresh, or freshly bled Ate Blue brake fluid before each DE. Also, the past two DEs I've done, I've used EBC Yellowstuff brake pads, which seems to be a decent compromise between track performance and cost.
I experienced no fade whatsoever at Road America with this setup this past July. Temps were 90°F+ both days out there as well. But then, I'm not going as fast as you are, either.
Cheers,
Jason