Ubuntu 13.04 and its derivative Linux Mint 15 were the fastest for the Smallpt renderer while CentOS 6.4 was right behind. Noticeably slower were Fedora 18 and Mageia 3.
For the final Linux test, a PostgreSQL database server comparison was done. CentOS 6.4 with its older kernel and compiler was the slowest of the six Linux distributions while the other EXT4-based distributions were running generally within a similar range.
Between Fedora 18, openSUSE 12.3, and Ubuntu 13.04 / Mint Linux 15, there wasn't too much of a performance difference between them. For CentOS 6.4 as the community respin of Red Hat Enterprise Linux 6.4, the performance was also generally comparable with this "out of the box" testing of each OS. There were a few areas though where the enterprise-grade distribution with lots of back porting had performed a bit more poor than the latest upstream distributions, but overall was in good standing.
The only distribution not performing like the rest was Mageia 3, which was generally slower throughout most of the testing. While Mageia developers or other interested stakeholders can dig deeper, one of the possible explanations for this distribution performing differently is it using a different CPU frequency-scaling governor by default for this Intel Core i7 Extreme Edition system. Any of the tests carried out can be easily reproduced via the Phoronix Test Suite and OpenBenchmarking.org.
In terms of the BSD distributions, for the source-based tests that were BSD compatible, PC-BSD 9.1 had a number of losses. The PC-BSD 9.1 performance may be attributed to using LLVM/Clang 3.1 as its current default compiler along with the old GPLv2 GCC 4.2, although other compilers are available through FreeBSD Ports. With the tests used, DragonFlyBSD 3.4.1 appeared to be in better standing than PC-BSD/FreeBSD 9.1 with our "out of the box" testing.
As said earlier, any questions about the test configuration and other feedback can be directed to the forums and Twitter. Requests for testing additional operating systems to build upon today's results can be made through those mediums.