Unbiased? Like Porsche?
"Yes, ve haff tested the M5... and while ve haff been able to do 7:50 with our Panamera Turbo, ve cannot get the M5 to go under 8:30."
"Yes, ve used the same drivers as vit our GT-R test. Why do you ask?"
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Considering no Ring time is actually "official", you basically have to trust that all times are done with standard cars. But still, third-party tests are not often as quick as manufacturer tests simply because the drivers don't have as much practice time in the car.
And then there's the surface, the weather, the traffic, etcetera, etcetera, etcetera...
I think the Hockenheim time (considering all laptimes are by Horst) is more indicative.