Phoronix: The Evolution Of Enterprise Linux Performance
Curious to know how the performance of enterprise Linux (RHEL, CentOS, Scientific, etc) evolves over time? Here's a look at the performance of Scientific Linux 5.7, the recently released Scientific Linux 6.2, and then Fedora 16 as representative of what will eventually work its way into Red Hat Enterprise Linux 7.
Most of these tests work out as I'd expect, considering that many of the changes to the kernel since the release of RHEL 5 have been for overall performance and/or multicore scalability.
This is definitely a compelling reason not to use ancient software, even on a server, assuming your server suffers any sort of significant CPU load. Personally I couldn't justify running anything older than RHEL6 on a server today, especially for new installations (large and complicated existing setups may justifiably remain on RHEL 5 until it's EOLed).