Benchmark Results: Audio/Video
Apparently, even one of the newer iTunes versions can't take much advantage of additional processing cores. Although audio transcoding is now pretty quick, this should really be fixed.
The same applies to Lame. It doesn’t scale well on multiple cores.
MainConcept wants as many processing units as it can get, although the improvements become smaller the more cores you add.
There are beautiful performance results in HandBrake.