I think one of these would be the new best choice:
Formula-GT - High Speed Ring (takes about 7 to 9 minutes to do the 10 laps, pays 210.000 Cr. + 200%);
Super Car Festival - Nurburgring (long lap, but pays 186.000 Cr. + 200%);
Real World Circuits - Nurburgring 24 hours (long lap, 226.000 Cr + 200%).