And if it's been explained 100 times already with the arguments you just gave, then I find those reasons to be in error. No one expects the absolute best-possible combination of settings in the benchmarks, but that's no excuse for using a provably slower default system when there are other common Linux systems with much better "default" performance (Ubuntu Studio, Linux Mint, Elementry, Pear OS, Arch, ect...). Using Arch is a logical choice because it's designed to be lightweight, fast, up-to-date, and easily customizable.
Remember, I never said that benchmarking a default Ubuntu system was a bad idea, only that it should be second to benchmarking a better Linux setup.
On a completely unrelated note (and not directed at soupbowl): I've ran a OpenGL vs DirectX comparison between Linux and Windows 7/8 recently on two dual-booted systems. The nVidia Card (280GT I think) got significantly better performance with GL on Arch Linux (100+ fps more) vs DX on Win8; however the AMD Radeon HD 4870 O.C. got significantly (as in ~half) the performance on Ubuntu 12.04 that it did on Win7. This was my own code, which largely tests pixel shader ops and render targets (barely any polygons), so take all that with a grain of salt.