Open-Source Nouveau Driver Remains Slow For NVIDIA's Fermi, Kepler
To no real surprise given past Fermi and Kepler benchmark results on Phoronix, the NVIDIA binary blob is running many times faster in general than Nouveau.
Hopefully Fermi/Kepler re-clocking support will come soon to Nouveau, but it doesn't look like it will end up being ready in time for the Linux 3.13 kernel, so it would still be several more months until seeing it in Linux 3.14 at the earliest.