I was just browsing and saw this post.
I too have an a6 s-line 2012. I also get around average 35Mpg, for the last 8000 miles I have driven.
I opted to go for a racechip after comparing the different mod chips out there. The reason I went for the racechip is that it was fairly inexpensive for the extra HP I gained from it, which states around and extra 41HP. I guess I'll have to tweak it a bit, but I can definately notice an improvement in driving.
The lag is gone now, the hesitation when you press the pedal to when the fuel is delivered. I can definately feel the performace is better.
