Small upgrade

Hello. Such a situation is that there is a computer with the following parameters Athlon x4 640, Radeon hd 5670 512mb, 4gb ram, and a power supply like 450, or. 550.
I will need to spend about half a year on it, and I would like to play something) completely upgrade, there is no way to spend money now. And here's the question: if I just change the video card, for some Bu, costing 50-60 dollars, (GeForce gt 640, Radeon 6670), can I play the latest games, and games of 15.14 years, at least at low ones, medium settings, hd resolution, but no lags, at least 30 - 40 FPS?
Or the processor will not pull everything smoothly, and there is no point in changing the video card?
Now, for example, dying light, at minimum settings, in hd resolution, is played with brakes. I think about 20 - 26 fps.
Thank you