Well, i finally got my Gigabyte Geforce GTX 780 Windstorm 3X and i'm pretty happy with how it performs with Nouveau.
(Of course Nvidia proprietary drivers will perform better...)
Unigine Valley with Ultra settings at 1366x768 gave me a score of 2718.
Yandere Simulator with Max settings runs at 25 FPS average at max settings instead of the 1 FPS i get with my GM45 graphics chipset lol.
Even with low settings though, it only averages at 30 FPS. I noticed that the game becomes slower despite having little to no graphical changes.
Dust : An Elusian Tale runs at 60 FPS (not a big surprise).
Kotu's tribute game still stutters, i guess he doesn't know how to use timers !
But anyway, i'll give Sonic Heroes, Sonic Riders, Billy Hatcher... a try later.