AMD RadeonSI Graphics Driver Still Troublesome On Linux
Xonotic failed to properly work on the newer Linux kernels with Mesa 9.3-devel, so the comparison here isn't too interesting since the kernel upgrades represent a bulk of the improvement to see in recent months for HD 7000/8000 series owners.
Plot3D in GpuTest on the latest open-source driver (Linux 3.11 / Mesa 9.3-devel) is at 33% the speed of Catalyst while the HD 7950 is at about 30%.