Even With Re-Clocking, Nouveau Remains Behind NVIDIA's Proprietary Linux Driver
These results aren't too different from earlier Nouveau vs. NVIDIA testing. Once re-clocking is fully figured out and working reliably, the results should be much better.
For those soon trying out the Linux 3.16 kernel with a Kepler GPU, the re-clocking support isn't enabled by default but needs to be manually set to the targeted performance state as outlined in the re-clocking article. Dynamic re-clocking will come later along with re-clocking for Fermi and other generations of NVIDIA graphics processors.
Tesseract is rather CPU-bottlenecked, but for the Kepler GPUs on the Nouveau driver is able to run close to the same speed between drivers.