The N20 engine in the BMW is also underrated (check out the F30 boards for more details).
Additionally, most of the grunt in the A4 engine is down low so I (based on my experience) find that it tends to lose steam as the speed rises. The transmission programming (in the 6speed at least) is not the most aggressive either in the Audi, even in S mode.
F25 X3 N20:
2010 B8 A4 2.0T quattro (current)/
2013 F25 X3 x28 N20 (babymobile)