Windows 8 makes better use of the CPU than 7 in general.
I'd suggest Win8.1 for everyone, as it is less bloated with services & software. In that way, it does make better use of CPU & memory, or rather doesn't hog it all for itself. Gamers can benefit nicely of it. But there are things that are messed up or conciously forgotten, like ability to customize your Windows. You have to delve into registry these days to modify how Explorer looks like and even that is not 100% working. If you don't mind the fluffy look and limit your desire to modify it to desktop background and window border colors, take it.
Think of it as a streamlined version of Win7. People worrying about that big bad start menu, don't. I almost never use it since all the software I need is in Taskbar or else. And you can sort it out, have all that Win8 Modern interface crap cleaned out. Few tutorial videos and you're right at home again.
What I like most about it is working sleep mode. Win7 sleep always broke up after a while and needed a fresh install to start working again. They fixed something about that in Win8. They took a right step with the background stuff and I think Win10 is going to be a good one.