Hello all. I just recently got back into UE after I built a new PC with Windows 10. This is a clean install from DVD and I am seeing serious performance issues in the launcher and editor. My FPS drops to below 15 seemingly randomly. Specs below, anyone else having issues like this? I just upgraded to 4.9.1 today and am still encountering this.
Make sure your Nvidia drivers are updated, there was a Windows 10 driver released recently.
I am currently on 355.82 WHQL 
Is there an option to enable DX12? Is that possibly the issue?
I doubt that will fix the issue though, might want to try to re-download/install 4.9 and try an empty scene or one of the free market place scenes and throwing some assets in.
So I just reinstalled 4.9.1 and created a blank project. If I hit play on the default scene the FPS counter is pegged at 120 but any time I try to interact with menus in the editor it drops to 5-7 frames. CPU utilization jumps to 30% for UE while the editor is focused, minimized it is reporting 1% (not sure if this is normal).
Random thought… Have you disabled the Skylake GPU in BIOS? Do you encounter the same issues with Unreal Engine 4.8.3? Updated Windows 10 (eg. for Z170 perhaps)?
The integrated graphics are disabled. I have not tried an older version but that will be next on the list. Windows is fully up to date.
EDIT: 4.8.3 exhibits the same behavior
I had an issue while using EVGA Precision X. It treated UE4 like all the windows except the viewport were background and ran at 10 fps (background default fps).
My system:
4670k (4.2)
GTX 770 4gb
Windows 8.1
16gb 1866 RAM
MSI Z87 board
I switched to MSI Afterburner and have had no issues.
Unfortunately I do not have any tuning software installed.