The only difference I see between Windows 8 and 10 which is relevant for gaming is in my opinion DirectX 12. Some games support it and it can give a bit FPS boost on them, depending on various variables. Thats why I upgraded from Windows 7 to 10. Everything else is not important for gaming. All in all, you can live with Windows 8 for gaming and it works quite well. I just recommend you to upgrade for free, as there is no real reason to stay at 8, other than avoid possible problems and work for upgrade process. Stay at 8, if you don't care DirectX12.