Building me a new gaming rig, Win7 or Win8?

[GeoTrail]

I am building me a new rig for gaming and such. So I'm wondering what is recommended for gaming, either Windows 7 Pro or Windows 8.1 Pro?
Here is the stuff I've ordered so far:

• Intel Core i7-4790K
• Corsair Vengeance Pro Red 32GB 2400MHz
• Corsair Hydro H110 CPU cooler
• Corsair Obsidian Series 450D PC case
• Corsair 1000W RM series PSU
• ASUS ROG Maximus VII Hero motherboard Z97 chipset
• ASUS BW-16D1HT/BLK/G Blu-Ray burner

And for graphics card I was thinking two Asus ROG STRIKER-GTX760 4GB D5 in SLI with a total of 8 GB of GPU memory.
I haven't built a PC in some years now, but I've done a lot of research about the components and they seem perfectly suited.
Only thing was which Windows version to run on the system. Which is most effisient for a gaming system.

[spacebuddy]

I use Windows 8.1 for gaming. All my games run well and I have no complaints.

I do play Diablo 3 most of the time, but I do have other games on Windows 8.1

[juror]

My son had me build a rig very similar to yours as a birthday present. He is primarily a gamer, online and on-the-box.

He has been very happy with Windows 8 and 8.1

He also uses it for math modeling software at college e.g. matlab and mathematica