I know this thread is old, but I have found that this is a common and misleading view. I have had S4s (B8, B8.5 tuned), currently have a B9 RS5 SB, and have driven most performance-oriented Audi models on the track including R8 V10+, RS7, RS5, RS3, TTRS, S5, S4, S3, TTS.
The S5 is a nice car...