Hi there triangle,
Yes GameFirst II will work in Windows 10, as i have tested this myself. What i found more intresting tho is that if you download (from Asus) the new Gamefirst III and you install it, it will work aswell with Crosshair V Formula-Z, as i used both programs, but ended up using Gamefirst III.
Note: The only thing i have an issue with GameFirst III is that u need to put it on Windows Startup folder, cause mine doesnt execute when logging into Windows.
So all and all, both programs work with both Formula-Z and Windows 10.