Honestly, linux is great for surfing and work (I do my HTML on it sometimes, use it at school cause it boots faster), but absolutely not for gaming.
If I may, why didn't you just save on other parts and got a license for windows with your computer (since you didn't want to pirate in the first place)? sometimes a shop will even sell you an OEM license (you'll have to ask, depends on the shop), which is way cheaper.
For windows 8...
Only because it's cheaper. I'd recommend W7 over W8 any day (when talking real computers, it works fairly well on tablets). I'm not even gonna bother getting a free upgrade for my laptop.