Nouveau Performance Is Faster With Linux 3.12
World of Padman and Reaction Quake 3 saw no major changes in performance with the Nouveau driver between the two kernel releases.
Xonotic with low quality settings at 1920 x 1080 was just 2% faster for the 9800GTX with Linux 3.12 but 7.5% for the Kepler GTX 680. The GT 220 here was about 11% faster on the soon to be released kernel.