It is not fair to say certain desktop environment is faster than others only based on fgl_glxgears’s output. There are many more factors than, just having some FPS gain in an opengl tool to consider a desktop environment over others. One more fact to consider, a distro which has say e.g. twm as default window manager might have more benefits (ease of use, performance) than running on Ubuntu. Following results reflect the output on my hardware, and might be different on yours even on similar setup.
Few years back, I was even unable to boot without using acpi off. When catalyst drivers started working on this hardware, it started to become better every time. With this new release the performance was even better. I was eager, how each desktop environment take advantage of this, so I wrote this article.