You can get w7 pro for $65 if you know someone with a student email. Pro also support 16gb+ like ultimate. There's really no reason for ultimate as the extra features are mainly encryption which sucks and you can get free encyrption that is better. All of them game the same, I doubt games will ever use 16gb ram before you pc is obsolete. Get home for the cheapest option, pro for 16gb+, domain join and xp mode, and ultimate if you have money burning a hole in your pocket. http://en.wikipedia.org/wiki/Windows_7_editions
This shows w7 getting more fps. http://www.hardwareheaven.com/articles.php?articleid=137
But there are other ones that showed no difference and even some showing a decrease. The world may never know but w7 has much more compatible hardware and software.