I tried watching Netflix and running a 3D benchmark (Heaven) at the same time on my Intel 640 onboard graphics. There is a ~10% drop in FPS. I imagine the performance hit would be negligible on a...

That is way overkill for cooling an i7-8700 that's not overclocked.

I have an i7-8700K, which is a 95W TDP chip compared to the i7-8700's 65W TDP, and I only have one 180mm case fan and one 120mm...