In recent days on Phoronix I have published benchmarks showing Windows 8 beating Ubuntu Linux for Intel Haswell performance and the Radeon Gallium3D driver losing to AMD Catalyst Legacy on Windows. As some good news for NVIDIA Linux users, the performance on Ubuntu Linux can beat out Microsoft Windows 8 on modern GPUs. However, the strong Linux performance can only be found if using the closed-source NVIDIA driver and not the open-source Nouveau alternative.
In years past on Phoronix when delivering Windows vs. Linux benchmarks with NVIDIA graphics, the performance has generally been comparable with the performance being more or less the same. With Windows 8 and the latest Linux stack, it's still largely this way but there are some nice performance wins too. However, if using the Nouveau driver, it remains a rather dire situation.
The open-source Nouveau driver developed through reverse-engineering still only supports OpenGL 3.1 rather than OpenGL 4.3 found with the latest NVIDIA Linux driver, the performance is largely behind, and as part of that the performance is horrible because most NVIDIA GPUs can't properly re-clock so that the Nouveau DRM driver can increase the core/memory/shader clocks to their designated frequencies and voltages. The Nouveau driver also has other shortcomings like needing to use external binary firmware for the video decode engine (VDPAU) support, some stability issues, and other problems depending upon the GPU.
While the Nouveau driver leaves a lot to be desired, it's the default NVIDIA graphics driver on Ubuntu Linux and other distributions due to its open-source status. Meanwhile, the proprietary NVIDIA Linux graphics driver is full-featured with performance spot on to their very well tuned Windows driver. The NVIDIA binary Linux driver shares mostly common code with the Windows driver (and Solaris/BSD).
On our Intel Core i7 4770K "Haswell" test bed, the NVIDIA GeForce 9800GTX, GeForce GTX 460, and GeForce GTX 680 graphics cards were tested. The 9800GTX was used as a graphics processor with very mature support while having a Fermi (GTX 460) and Kepler (GTX 680) graphics cards is interesting for a modern look. The Nouveau driver has no support for Fermi/Kepler re-clocking support yet and when attempting to re-clock the 9800GTX on the Linux 3.11 kernel there were artifacts and stability problems under stress.