Higher framerates in CS:GO are actually more because of the GPU. It could be that it is temporarily overheating and throttling to prevent damage. To check this please could you tell me the CPU and GPU along with the power supply.
Both AMD and NVidia use software and I believe they can both be used to limit the framerates. I have an R9 280X and was running CS:GO at around 210 FPS but because my GPU was getting into the high 60s in degrees Celcius and heating my leg up I limited my framerate to 120.
If your GPU is getting to around 90 degrees Celcius then this may be the issue depending on the model. 110 FPS still gives smoother gameplay than default vsync for most monitors but should prevent thermal throttling.