When the Nvidia In-game overlay is enabled it appears to cause performance issues with the editor. If the editor is open before the overlay is enabled it does not seem to cause any issues.
I stumbled across this when helping some users with FPS issues in their projects.
This is just a very basic way to showcase this, FPS drops are persistent in just about every aspect of the engine when this overlay is enabled.
Head over to the existing Questions & Answers thread and let us know what's up.