You are cpu limited.
Most games are limited by the performance of the single master thread.
Task manager utilization can be very misleading.
Windows spreads cpu activity from one thread among all the available threads.
Your games are likely only using 2 or at most 3 threads.
X4-760K has a single thread passmark rating of 1437. Virtually all amd processors, including FX-6 and FX8 have single thread ratings in the 1500 range.
If you want to do better, plan on changing to a Intel cpu.
The I3-6100 would be a nice boost, it has a single thread rating of 2102.