Sabayon / Gentoo-based
Manjaro / Arch-based
Debian sid. Aren't most distros based on Debian if you compare the numbers? It's used on servers and tweaked and Ubuntu used to be Debian-based.
Since, they use the 'non-free' ethic, any of the tests and configuration would be more useful to the Linux community since people would become more familiar with actually using their OS. I mean, the additional tweaking illustrates the internals and configuration required. Of course, the Ubuntu OOTB convenience is good but Canonical/Ubuntu are going off the road more and more so I'm not sure it's a good pick as the 'official' choice for benchmarking.
Just my two cents.