AS far as I remember EF goes to the AC_VI, aka video queue, that should be fine. Unless you have a heavy user of the voice queue already, but then also using AC_VO will only make things slightly better, as your game packets will not be able to jump ahead of those, it will just be able to compete with them on an even playing field...
Here is a quick way to test, using putty as an example (these commands need to be run in a powershell terminal under windows 10 that was started with the "run as administrator" option):
# set putty to use dscp 46 aka EF on egress temporarily:
New-NetQosPolicy -Name "putty_ps" -AppPathNameMatchCondition "putty.exe" -PolicyStore ActiveStore -NetworkProfile All -DSCPAction 46
# show all defined NetQosPolicies (should show the just defined putty)
Get-NetQosPolicy -Store ActiveStore
# for the fun of if change to dscp 47
Set-NetQosPolicy -Name "putty_ps" -PolicyStore ActiveStore -NetworkProfile All -DSCPAction 47
# clean up
Remove-NetQosPolicy -Name "putty_ps" -PolicyStore ActiveStore
Note that omitting -PolicyStore ActiveStore should make the settings persistent...
See https://docs.microsoft.com/en-us/powershell/module/netqos/new-netqospolicy?view=win10-ps for more documentation. For all I know this might even work on windows 10 home and maybe Xboxen...