Drop your resolution to 720p and medium settings, then run the game benchmark and note the framerate. Now raise the resolution to 1080p, leaving the settings the same and run the same game benchmark. Is there a big difference in framerate? This will tell you what that game needs. If the framerate is much higher at 720p, you could use a videocard upgrade. If the framerate is pretty similar no matter which resolution, you could use a CPU upgrade. This only applies to this game you benchmarked, you'd have to repeat this for each game you are wondering about.
For certain games, having a real quad core as opposed to hyperthreading will increase your framerate. The problem is that increase might not be all that much at 1080p using that 970...