High Perf Theme
Since we're focusing on performance the most optimized theme in windows 10 is high contrast mode, just without the ugly. Theres tons of them out there even night mode versions available or you can make your own. But setting the high contrast mode essentially drops all the gpu-using fancy desktop composition from running alleviating some strain on resources and bringing back some system responsiveness. The OG user made the basic classic theme a long time ago and it still works on windows 10. If I get time I could port over my old 3dcc dark themes for this, I also heard jasmine 3dcc might be getting updated for windows 10. Alternately you can quickly make your own by clicking on the style from the personalization window and clicking "color" to bring up the color picker menu, then save your own style.
All theme files save and get installed to:
C:\Windows\Resources\Ease of Access Themes