You want a max speed tune.... This applies to any car: floor the suspension, set tranny to the highest speed setting possible, no downforce, and that's it!
I actually found that the Cien is really good at SSR7 and Le Sarthe when it is nearly stock in regards to settings. It handles pretty good, and the downforce doesn't cause that much drag.
Ssr7 is literally all straights, with a couple of super high speed turns and two hairpins, downforce and turning ability don't really matter there... It's like the way "Like the Wind" was in GT4