Even the notion of a Ring Time Cup for manufacturers makes little sense. There are just way, way, way too many variables. If you go to VIR or Laguna Seca, the only typical variation you'll have is whether the track is green or not. If you go same day/same driver, you're going to get a decent comparison between two cars. You're not going to get from one end to the other and have totally different ambient temperatures, barometric pressures, rain, sun, constantly altered surfaces. They are constantly repaving and repairing the Ring. They just leveled out a little bit of the areas that used to result in air time at high speed.
There are so many variables and so many corners, that outside of marketing or vehicle development, it's nonsense. It's a very useful tool for manufacturers in testing because it's a punishing environment, but it's one that is ever-changing, so all the arguing over Ring times is apples/oranges. Plus the people who do the marketing are never going to do it in a truly factory showroom stock car.
I would like to see the Performante at VIR. If it's capable of a 6:52 at the Ring, it should be deep into the 2:3Xs.