As the last test from the System76 Galago UltraPro Intel Haswell ultrabook prior to returning the sample to System76, I installed Kubuntu 13.10 and ran some tests from KDE 4.11.2. For the test I compared the Linux OpenGL gaming performance with the stock Kubuntu desktop and then re-running the tests after enabling the "suspend desktop effects for fullscreen windows" feature inside the desktop effects system settings area for KWin on KDE 4.11.2.
The Kubuntu 13.10 system was running the Linux 3.11 kernel with Mesa 10.0-devel. Full results along with the complete system hardware/software details are available on OpenBenchmarking.org via 1310217-SO-KDESC411D84. All of the gaming tests were run in full-screen.
From these Linux OpenGL Kubuntu gaming results and others in the aforementioned OpenBenchmarking.org result file, there's no longer a big performance gain from being able to disable KDE's desktop effects when running fullscreen windows/games, at least for Intel's open-source driver with Core i7 Haswell hardware.