GT3R and GT3 Cup are spot on and simply amazing! Cayman Clubsport is fine, while the rest seem like slightly refined versions of Kunos original sounds. Unfortunately, I keep getting the crackling effect that seems to plague Fonsecker's sound packs, no matter how much I adjust my settings. It's more prominent in the standard cars than the racing cars, though. Also, I miss the metallic roughness of the original 911 RSR even though the exhaust tunes sound somewhat better with this pack.
Sure, this is not 100% real but i prefer high quality samples, cause the 997 cars have not that loud transmission sound as the 991 have so i was able to create better engine samples.
But as usual, i am sure i will update the sounds in the future if i find better recordings.