Starting off by measuring the time needed to compress a 256MB file using LZMA compression, there really is not much to say. The Linux 2.6.24 through Linux 2.6.29 kernels had performed roughly the same. No improvements, but no regressions.
The 7-Zip compression performance had fluctuated much more between kernel releases. After the Linux 2.6.24 kernel release, the performance regressed in each release up until the Linux 2.6.28 kernel, which performed the best. With the just-released Linux 2.6.29 kernel, the performance faltered to the lowest score in any of the past six kernel releases.
The LAME MP3 encoding performance was maintained across the tested Linux kernels.