GPU performance drops during stress test with the GPU and CPU, why? | The hardware community for PC gamers

Hello everyone!

I’m wondering about a stress test of my CPU and GPU with Furmark.
If I also start the CPU Burner for the GPU stress test, the GPU clocks down from approx. 2000MHz core clock to about half (see image).
I ask myself why?
The maximum temperatures during the stress test:
CPU: 74,3°
GPU Core: 68°
GPU Hot Spot: 103°

My CPU: Ryzen 7 3700X https://geizhals.de/amd-ryzen-7-3700x-100-100000071box-a2064553.html?hloc=de
Mein CPU Lüfter: AMD Wraith Prism https://geizhals.de/amd-wraith-prism-712-000075-a1980869.html?hloc=de
My GPU: Sapphire Radeon 6700 https://geizhals.de/sapphire-radeon-6700-11321-03-20g-a2747045.html?hloc=de

Thank you in advance for your answers!