The World of Padman result is similar to that of the other ioquake3-based Linux games on Nouveau.
With the Warsow game, the frame-rate of Nouveau even ended up exceeding that of the proprietary NVIDIA driver. To the human eye, the rendering quality was similar between the two Linux GPU drivers.
The DarkPlaces-powered Xonotic performance was also decent when factoring in the clock differences between the drivers. It will be interesting to see how the Nouveau Gallium3D performance compares to the NVIDIA binary driver when the re-clocking situation is all sorted out. There's also other discrete NVIDIA GeForce graphics card tests under Linux on the two drivers that are forthcoming on Phoronix.