An independent Phoronix Test Suite user has been uploading large amounts of test results to OpenBenchmarking.org of different desktop / graphics driver options and their impact on graphics tests. Here's the latest results including runs from GNOME classic, GNOME 3, GNOME + Openbox, Lubuntu, Openbox, Unity, Unity 2D, KDE Plasma, Xfce, and other software configurations. The tests from this user not affiliated with Phoronix.com was running from a NVIDIA Quadro NVS 160M graphics card. The user also tested Ubuntu 11.10 and the current Ubuntu 12.04 state.
Thanks to the Phoronix Test Suite and OpenBenchmarking.org, anyone is able to easily reproduce these comparisons. The tests being carried out by this user are mostly with the gluxMark test profile.
See the results in full on OpenBenchmarking.org plus the many other "Desktop effect on OpenGL performance" benchmarks you can find from this user via OpenBenchmarking.org.
For comparison, there's my results from earlier this month and similar tests from last May.