Every attempt, on this topic, to try explain why your game is slower when u overclocked your CPU are elegant but wrong. Nice try thought.
When u overclock an integrated circuit the performance gain is not linear but we can approximate it. If u rise the CPU clock speed by 10%, lets say that at the same temperature (of the processors with its original clocks) the performance gain would be 5%. But we know that the chip (on a complex circuit, like a computer, not only the chip u are overclocking will rise its temperature) will produce more heat, then the real performance gain will be 5% minus the percertual lost due more transistors now being used to compensate the temperature difference.
Of course there is a lot other factors involved here but like I said we are approximating.
This approximated function of performance gain Vs clock speed (teorical gain minus % lost due transistors used to compensate the temperature rise) gives u a non-linear curve, with a maximum as critical point.
That mean that after the maximum point, if u keep rising the clock, the temperature will make your chip downgrade due the high number of transistors that now are used just to compensate the temperature on the circuit.
This is not necessarily caused by your CPU temperature, its mainly caused by the memory controller temperature that in your motherboard controlls the communication with the graphic card and other components as well.....When u overclock your processor, the memory controller will work a lot harder and out of its original specifications and that may downgrade its performance making your computer a lot slower.
Thats why high end power suplys (that use components with low tolerance) and high end motherboards are often used by proffissional overclockers. Of course this hardware need to be paired with high end graphic cards and CPUs but intel, amd, nvidia are happy to be part of a small group that hold top technology on this matter so if u are overclocking u need make sure u have a good power suply and motherboard bcuz graphic card and cpu u probably alredy have.
Also, your hardware seems good to overclock, I just wanted to correct the argument that some ppl are using - saying that overclocking a CPU will make the game slower if the bottleneck is the GPU. By that u could say that upgrading your CPU will make your game slower if u the GPU is not enought to bring FPS up and thats an absurd but u guys did a good job trying to guess, keep going.
Your problem seems like not a problem, I would say +-0.1 FPS is not to be considered, its a small error margin. You should repeat the test several times and then divide (total fps)/(number of times). Thats how its done by professional benchmarking tools.
Im sry for the terrible english.