I have Nvidia GTX 850M 4Gb DDR3 but I overclocked it +135mhz/+180mhz which gave me +15%/20% performance gain and it`s now equivalent to GTX 860M.
My settings in GTA: 1920x1080, FXAA, textures and water on very high, post fx on normal and everything else on high. My framerate goes between 30 and...