I found this post on the Roadfly.com Z8 Messageboard:
Laptimes for different cars
Here are some times for different cars. A quite interesting list to read.
The information was compiled and sent to us by David Mocnay, who got the times from the German car magazine Sport Auto. We send our thanks to David!
The laps where all done by the same driver on a dry track at Nuerburgring Nordschleife.
Car Time Comment
Porsche 996 GT2 7 min 46 sec
Porsche 996 Turbo 7 min 56 sec
Lotec Porsche 993 Turbo 7 min 57 sec 600 HP, racing suspension
Porsche 996 GT3 8 min 9 sec
Ferrari 550 8 min 7 sec
Lamborghini Diablo SV 8 min 9 sec
Ferrari 360 Modena 8 min 9 sec
Chrysler Viper GTS 8 min 10 sec
Porsche 993 Turbo 8 min 12 sec 430 HP version
BMW Z8 8 min 15 sec 400 HP
Porsche 996 C2 8 min 17 sec
Ferrari F355 8 min 18 sec
BMW M Coupe 8 min 22 sec 321 HP
Audi RS4 8 min 25 sec 375 HP
Porsche 993 C2 8 min 28 sec
BMW M5 8 min 28 sec 400 HP
Porsche Boxster S 8 min 32 sec
BMW M3 Coupe 8 min 35 sec 321 HP
Honda NSX 8 min 38 sec
Honds S 2000 8 min 39 sec
Chevrolet Corvette 8 min 40 sec
Audi S4 8 min 42 sec 265 HP
Lotus Exige 8 min 42 sec
Jaguar XKR Coupe 8 min 49 sec
Mercedes CLK 430 8 min 52 sec
Note that the Z8 beat the Porsche 996 C2 and the Ferrari F355, and the M5 beat the M3 coupe and Corvette (not sure of the model). The BMW brothers held up pretty well against the impressive field of race-bred Porsches, Lamborghini, and Ferraris!