Glad it helps some of you. I honestly do not know if it has something to do with HT as the CPU I have (the I5-8600K) has no Hyper Threading and I have not looked into the 8700K but assume it is the same. @WeamDreaver What other settings do you have. I fiddled arround some more and even though the CPU has overhead now I cannot push all settings to max.
Aside from the xxxxK family for people who do have HT: Disable HT and then untick one core in the taskmanager?
Regardless I will try some more comparising tonight but for me it was a relaxing evening last night flying around.
@CorsairDriver: Start flightsimulator the regular way. Once booted Alt-Tab out to Windows and start your taskmanager (either ctrl-alt-del > Taskmanager or right click taskbar and then taskmanager) and find the process of Flightsimulator. Then go to the detailsl of it and you will see Flightsimulator.exe. Right click it and you’ll get a drop down box. Select Affinity and unselect (untick) a core. I chose the last one on my 6-core wich was core 5. Press OK and alt-tab back into the sim.