I agree with AUnlikelyPotatoe .
What is happening is the cpu when it reach a certain temperature it starts throttling, which means the frequency and everything slows down to protect the processor, and therefore it will be very slow, it will affect everything.
I myself have an 4790K @4.6GHz with a Noctua C-14 with dual 140mm fans and the cpu has never been up to more than 65 °C even while playing Crysis 3.
So,a good cooler is a & o.
If You are running with the stock cooler, it still should not reach those temps, so I'm thinking perhaps it is not correctly mounted?
Please see this video of how to correctly mount the cpu and also the cooler.
Take a close look, because it could be that it is where your problem resides.
This video is showing this absolutely correct:
Install an Intel LGA1150 or LGA1155 CPU Processor as Fast As Possible
Pay close attention when it comes to the mounting of the cooler.
Best regards from Sweden