The i5 2500K comes with built in Intel HD 3000 Graphics. The low framerate seems to indicate to me that it may be using the onboard graphics rather than the GPU.
An unstable overclock could cause performance issues. Even if it's not unstable, some games don't play nicely with OCing. For example Battlefield 4 crashes on pretty much any GPU overclock. A 4.2 GHz OC is pretty high for a 2500K.
I dont have it in my components list thingy on control panel, so I dont know how to deactivate it then.
I usually when starting up my PC while playing any heavy games, turn on MSI afterburner with around 300Mhz OC and 110% power limit, no problems with BF4. Although its all stock on COH2.