For your specific needs, the 965 will be plenty, but to max highest settings 1600x900 a 750 is no enough.
r9 280 is a great budget card that handles ultra at 1080p for any games out there.
r9 270 is good enough to get max setting on 1600x900 for gta V, and is a great budget card that can run high/ultra (no post proccesing) settings 60fps 1080p on any game out there. (not 270x as they are identical chips with different clock speeds=money wasted)