Toyo R888 I always found to overheat on track after 10 mins.
The new R888R are ment to be much better and not overheat as easily.
Kumho V70 are better IMO. I ran a 225/45 a little while ago when I was on 16" wheels.

Have you found Mike Rainbirds posts from the past on here advising of road and track setup parameters. They were also in one of the FastFord magazine articles on Cossie setup, probably available on Mikes (R&B Motorsport) website and FastFords.