The 1.4.1 release notes has this:
 Performance has been improved significantly on 64-bit non-Linux and
non-Windows platforms (generally 10-20% faster compression and 5-10%
faster decompression.) Due to an oversight, the 64-bit version of the
accelerated Huffman codec was not being compiled in when libjpeg-turbo
was built on platforms other than Windows or Linux. Oops.
So our OS X client would benefit from this.
Upgraded in r30701.
Can't see any real performance increase from this, most likely because bug 5415 is dominating CPU usage. It is not worse either though, so the upgrade can stay.
Ran old and new client and used instruments for profiling. There was a big difference how much time was spent in huffman encoder.