Well, I had 7 and I can tell you that 8 isn't more resource hungry, 8.1 is good, 8 without the .1 sucks btw.
Windows 7 has slightly higher max framerates, but also large fluctuations in those framerates.
Windows 8 has just slightly lower framerates but more consistent.
windows 7 is optimized for old school spinning hard drive IO, while 8 is tailored for SSDs and works awesomely if your gonna get one.
8.1 also can be running the desktop all the time if you hate metro. All the basic functions like control panel and whatnot are pretty much the same as 7.
someone had mentioned that i should go with windows 7 since it is better for gaming and is very stable and it is not a hungry-resources OS.
windows 8 is better for gaming than 7.
actually windows 7 supports directx11.1(End support from Microsoft) and windows 8 will support directx12 (as microsoft said)
Nothing wrong with windows 7, either OS is fine and both can upgrade to windows 10 for free when it is released later this year, so just pick one already lol