The CPUs I mentioned above would be your only hope. Any Phenom II x4, x6 in the list in the link that are faster then the Athlon II X4 you have now. That said, the clock speed difference won't make as much difference as the fact that you will be gaining an L3 cache with the Phenom IIs.
But if the upgrade is mainly for gaming, a gfx card upgrade will provide the biggest performance boost. Unfortunately as I mentioned, gfx cards are outrageously expensive right now due to the crypto-miners and the surge in Chinese gaming.
The GTX 1050 Ti would give you a better performance boost than say a Phenom II X4 980
Nvidia GPU Upgrade:
http://gpu.userbenchmark.com/Compare/AMD-RX-460-vs-Nvidia-GTX-1050-Ti/3641vs3649
AMD GPU Upgrade:
http://gpu.userbenchmark.com/Compare/AMD-RX-460-vs-AMD-RX-570/3641vs3924
CPU Upgrade:
http://cpu.userbenchmark.com/Compare/AMD-Athlon-II-X4-640-vs-AMD-Phenom-II-X4-965/m225vs606
If your biggest slow-down is online gaming on busy servers, then the CPU would help more-so than the GPU. If you are a single player gamer, the GPU would help more.
The best thing would probably be to wait until prices stabilize again, and then go for a new build with a modern platform.