When trying to play Mass Effect 1 as part of the "Legendary Edition", I encountered horrible performance, but only whenever I moved my mouse even the slightest. This issue might also exist with the original version. I have not tried.
As u/phineas42 pointed out in a comment to this reddit post the issue was that I enabled Hyper-V Virtualization inside the Windows guest in order to fool some Anti-Cheat systems, which did not allow running the Game in a VM.
So to get a smooth Mass Effect Experience, I had to disable Hyper-V Virtualization inside the guest again. Maybe this helps anyone else. Cheers.