I think you and I are on the same path here, my passenger side sill has a few places where the paint has bubbled off because of the heat, so my plan was to insulate the side sills and that might have worked if not for the adhesive backing smoking when my car gets up to temp.
Because of that I'm going the ceramic route and I'll test the sill temperature when hot and see what it tests at. Once I'm satisfied, I'll get the side sills, front and rear fascia's repainted and be ready for VOI 11.
I might still do headers and high flow cats later this fall or winter, but if I didn't solve the heat issue now it would have been wasted money to not engineer some cooling now.
Regards,
Aaron