I've been racing a 1st gen on Illuminas for a few years now. They do exactly what they are supposed to, and the adjustability is nice (soft for a long cruise, hard for playing). And I've been doing quite well for myself with this setup, with frequent wins in CSP against Miatas on race rubber (I run $45.00 tires). Lots of videos linked in my signature if you care to check them out.
However, have you considered Bilstein? I don't know whats available for the 8, but last year I replaced my rear Illuminas with Bilsteins and I have to say, although they aren't adjustable, they perform flawlessly. The back end is at least as firm as the Illuminas, but just seems a lot "stickier" than with the Illuminas. There was a definite performance increase with this change.
If I ever move away from Illuminas on the front, then I will be going with Bilstein. In my opinion, they are a much better shock than Koni, and they can be rebuilt by the owner rather than having to send them out for changes or repairs.
Good luck with your project.
.