I experience this too. I assume that the engine is drawing any other window per frame and impacts testing. Frame drop also happens if you have a viewport but launch a window to play it as it renders a static viewport while also playing the game. I will keep all my windows docks as you say and switch my viewport to the output log when I test. I’ve gotten use to this over the years and assumed its just engine limitations. Either way, editor frame rate is not dependable even with these fixes. Standalone or a packaged build will produce correct testing performance.