Hey all,
Just read this tips from RPS (about fixing XCOM2 performance which is based on UE3) and I found that tips #7 can be applied to UE4 editor as well. After applying tips #7 to UE4 editor, I see less spikes in the performance stats, and UE4 editor is also running a lot smoother and snappier than before. Of course your mileage may vary, but in my case it really does help to optimize UE4 editor.