As anticipated, it looks like Windows 10 offers little to no performance advantages over previous versions when it comes to DX11 gaming, at least not in BioShock.
Surprisingly Windows 10 provided consistent gains in Metro Redux with the GTX 980. This could simply be an issue with the drivers though.
Performance slightly drops off in Hitman when moving from Windows 7 to 8.1 and then to 10.
Tomb Raider delivered the exact same performance across all three Microsoft operating systems.
Finally we have Crysis 3 and here Windows 10 performed well, delivering strong performance at both tested resolutions.