Trying to hit constant 240fps

So I'm trying to get a constant 240fps but I can't figure out why sometimes it'll drop down by ~100fps while GPU and CPU utilization are nowhere near their limits. Most of the time it runs at 240fps and normally I can see the GPU at ~90% when it drops below that but then there are these weird drops that I can't find a cause for.

In the image below you can see what I'm talking about. I'm currently playing on a CRT 1280x1024@120hz, I don't need the 240fps now but I'm testing the system to see if I should get a monitor that fast. CPU is 4770k@stock since overclock gave me stutters in-game, GPU is GTX 1080FE OC'd and I've got 16GB 2400mhz DDR3.

You can see the GPU is at 68% utilization and the CPU has plenty left while at 157fps. Might this be a bottleneck in my system or a matter of the game performing badly?

Thanks.