Doc,
The Nordschleife is something very dear to my heart.After spending a wonderful Saturday there in 02, I can say that a lap on GT4 is VERY close.
The best way to descibe it is Mt Panorama X 3, with a boom gate and $20 for a lap.
NO RESTRICTIONS 'cept for noise.Sabine's* 500hp Beemer is booked out a full 18 months in advance, let me tell you punters get out of that fairly white. wobbly legged and pretty quiet.
I took the Volvo hire car around, got a lap with Simon the Pom in his Lotus Elise and the crowning glory was 'Frank' a Mercedes salesman in a Opel wagon.Suffice to say he was seroiusly quick(11min) we were only passed by a Porsche GT3 and a Ducati 916.Frank would slam the anchors on 70m from a corner from 220k's turn in, floor it ride the inside kerb and let it drift out to the outside kerb for a full 20km.All the while giving me a running commenatry of the corners and points of interest in English.
Very abridged version, as I could burn all the available bandwidth crapping on about the things I saw and did that day.
* Sabine is HOT and owns a pub