PR refers to overall performance, alright.
But as shown below, compared to the 2015 911 RSR, the 2017 version is slower and takes longer to accelerate and stop (for that particular level of upgrades). The 0.01 g better lateral grip can be neglected. However, it has a PR 1.5 higher. How would that make any sense?

Would it be that the handling advantages of the Mid Engine doesn't show in the car specs actually (as if the PR reflected dynamic capabilities of a car, which doesn't), or... Monkey Engineering?!