I dont have a constant with my TCS, tires or quick tune, but i do only use automatic. I do that because I can.
My times @ Nur:
1) Ferrari F2007 - 6'03.016
2) Audi R8 Race Car '01 - 6'51.925
3) Bugatti Veyron 16.4 (SP Model) '09 - 7'10.673
4) Chevrolet Corvette C5-R '00 - 7'23.302
5) Chevrolet Corvette ZR1 '09 - 7'25.022
6) GT by Citroen '08 - 7'25.791
7) Pagani Zonda C12S '00 - 7'28.080
8) Mazda Furai Concept '08 - 7'31.342
9) Enzo Ferrai '02 - 7'32.519
10) Mercedes-Benz SLR McLaren '03 - 7'35.246
UPDATE July 16 2010:
I recently got some better cars and actually tuned them (all above are default quick tune). Now I have all sub 7 times.
Ferrari f2007. 5:43:858
Bentley speed 8 race car '03. 6:23:729
Audi r8 race car 2005. 6:24:172
Pescarolo c60 hybride race cAr 2005. 6:24:268
Audi r8 race car 2001. 6:27:801
Polyphony f1. 6:28:521
GT by Citroen. 6:49:769
Pagani zonda LM race car. 6:50:931
Chevrolet corvette c5-r 2000. 6:54:367
BMW Mclaren F1 GTR race car 1997. 6:54:474
All: tcs:3 asm: on. Active steering
n. Quick tune: default except rear toe angle (-20 to -40) (all default on f2007)
I know I cheated with the driver aids but I don't care. I really thought my times sucked until I saw all these plus 7 and 8 minute times.