This may depend on hardware and requirements. Windows 10 works better for USB 3.0 capture card on intel USB 3.0 controller with default USB drivers that came with windows 10. Some USB 3.0 capture (Elgato HD60-S) have "Windows 10" as part of requirements. Future games may soon drop windows 7 and below.
The one thing windows 7 have is the ability to turn off DWM (Desktop window manager) which was called Aero. When this is off, this allows having nearly no delay for gaming in windowed mode.
DWM on windows 7 and 10 still does not work nicely on multiple monitors of mixed refresh rates where one monitor is 60 Hz and the other at 75 Hz, resulting in an overall 60 fps making one monitor always jitters, or sometimes jitters if primary is at 75 Hz. I have managed to get all my monitors to 75 Hz so it is now smooth without much issues.