Another thing to check is to look windows control panel and power setting and use high performance mode (those power saving modes can some time leave processor to lower GHZ and that causes stuttering just like mentioned). I hand same problem in my gaming pc with amd ryzen x3700 that some time cpu is stuck in 300mhz in power saving mode and would not rise cpu clock when inq martyr starts and goes to main menu ( and stutters like crazy). Forcing the hig performace mode fixed problerm in my end.

I would recommend you to check on your Video settings in the Main menu. Disabling Frame Blending and Temporal AA can have a huge impact on your performance.