NVIDIA Fermi/Kepler GPUs Are The Best Bet For Ubuntu 14.04 Nouveau
Due to the Nouveau re-clocking issues, even high-end GeForce 600/700 series hardware can't even run the id Tech 4 powered Prey out-of-the-box on Ubuntu 14.04 LTS.
Obviously the Unigine Engine tests struggle greatly due to the reclocking challenges of Nouveau.