The performance difference between your 3 options is not much, but price difference is considerable. but i think 780 ti SLI will perform better in comparision to the options given, but if you are gaming at much higher resolutions than normal and turning AA(anti-aliasing) very high then the r9 295x2 is better because of the 1024-bit and 8 gb of VRAM. 780ti in sli outperforms the r9 295x2