I've been doing track driving for maybe 15 years now and am enthusiast in terms of comparing drivers and cars on track (actually started one time attack series 10 years ago that is still popular among track drivers, but that's another story.. ) Have been nowadays going more to Alastaro that is quite popular track as it has good safety areas, and track provides both fast and slow corners. Track has three long straights so it favors powerful cars.
At the moment on short variation GR seems to be 2s off from Mk1 GT3 (390hp) and 3s off from Mk1 GT3 MR (+400hp).
Not beating them yet, but it starts to be in a ballpark where you can start teasing heavy weight track cars, Especially it has quite bit less power than those GT's, and lots of less tire (using stock sizing 225mm cup2 at the moment).
It is now actually quite fun to drive around - not caring too much the times (even though enjoy timing all the laps), but the car has started to work according drivers inputs that is always a great thing!
With a same power levels I'd say GR is quite fast car, and can keep up with any car with same hp.
btw didn't hear any times from those AMG's in same picture but guess they were slower.