Audio/Video Benchmark Results
iTunes wasn’t optimized for multi-core processors, but it scales with faster clock speeds. The step from 3.33 GHz to 3.9 GHz provided only a little benefit, but going to 4.26 GHz introduced a nice speed bump. iTunes seems to be sensitive to memory performance as well, which could explain the poor performance at 3.6 GHz when compared to 3.33 GHz.
Lame also scales nicely as you beef up the clock speed.
DivX is faster at transcoding video with every clock speed increase.
Xvid benefits even more from faster clock speeds than DivX.
The MainConcept encoder also was optimized for multi-core processors. Using a quad-core CPU will probably give you much more performance than the overclocking efforts we went through.