Yes, I don’t really expect the volumetric vanilla clouds to run smooth. The ones derived from Burks material i made are already performance killers.
I made a copy of a secondary scene I had and replaced the skysphere with the athmosphere system+volumetric fog.
the problem with benching it is that in order to get an accurate measure I think I need to run 2 project versions (because of project settings).
Offhand it seems that the volumetric fog with the sky atmosphere setup is more expensive then the defaullt version using the same settings.
In FPS terms by a lot. From around 100 down to 70.
However when running in pie this cost seems to go back to where it should be, so its a bit confusing.