Depends on the game title, but your CPU is starting to show its age. If you ran like 4K at the highest settings on an older title, maybe. Anywhere you are GPU bound. But if your CPU is always at 100% a new GPU isn't going to improve things much.
I would spend the money on a new platform before replacing the GPU. Or do both at the same time if you have the cash.
Basically you need to set a target. So like BF1 at 2560x1440 at 75Hz. That is going to take a lot more CPU and GPU. Minecraft woud be more CPU/Memory. Or if you only play games like LoL or DOTA2, well I'm not 100% sure there, haven't checked out anyone playing that title with a Phenom.