LAME MP3 encoding
We used LAME 3.92 to encode a 101MB 16-bit, 44KHz audio file into a very high-quality MP3. The exact command-line options we used were:

lame --alt-preset extreme file.wav file.mp3

Here are the results...

The Pentium 4 comes out ahead here. Barton's cache size increase is simply immaterial for LAME encoding. The fastest Athlon is the 2.25GHz T-bred, which has the highest clock speed of any Athlon XP. The T-bred 2600+ and Barton 2800+, at the same clock speed, turn in exactly the same encode time.

DivX video encoding
For this test, we took a 279MB video file, encoded in MPEG2 format at DVD quality, and converted it to a 33MB DivX file. We used the "medium" quality/speed setting on the DivX encoder, and we turned off audio processing. Otherwise, all settings were left at their defaults.

The Pentium 4 has long owned video encoding, and today is no exception. Once again, L2 cache size doesn't seem to matter much, and the T-bred 2800+ tops the pack of Athlon XPs. You can also see the striking benefits of Hyper-Threading on the Pentium 4 here. Adding a second logical processor cuts encode times by half a minute.