will the be a good preformance gain to go from a 7950 to 770 GTX or R9 290 X whit this build ?
http://azerty.nl/winkelmandje/winkelmandje/?legen=1&product%5B528532%5D=1&product%5B563039%5D=1&product%5B455750%5D=1&product%5B563658%5D=1&product%5B447319%5D=1&product%5B398419%5D=1&product%5B556542%5D=1
I would keep the 7950 at this time. The R9 will be faster, but the 7950 is such an awesome card.
It's not worth upgrading to a 770 gtx from a 7950, that performance increase can totally be achievable by overclocking the 7950. When it comes to the 290x, well, the performance increase will definitely be worth it IF you are playing at higher than 1080p, if you are just playing at 1080p the 7950 is a beast and you can play even at 1440p max games like bioshock infinite or lower, for crysis 3, metro etc. you would have to lower the settings a bit. I don't know for sure, but I would not suggest pairing that fx 6300 with the "titan killer", bottlenecking may appear.