I personally never adopt a Microsoft OS prior to Service Pack 1. I've beta tested 8 and just simply do not like the interface formally known as Metro. It is designed with touch screens in mind and you do not get a START (in Vista and 7 that windows logo) button in the bottom left corner. There are alternative ways to access that stuff, but was not friendly to me at all. It will take getting used to, but for me there is no real advantage to 8 right now for a desktop, or laptop, that at the least doesn't have a touch screen. I get it for tablets and phones, it makes sense. That last paragraph was all personal comments so don't let that sway you. Performance wise it will be fine.
BTW, there are 3rd party apps you can purchase that create a START button for you. It has probably 80-90% of the normal functionality. I think some of the right click options are missing that were natively there in Vista or 7.
I just upgraded from Vista to 7 after 5 years. Never had a single issue with Vista. Never knew why everyone else complained so much. It is perfectly fine. 7 is just Vista (ver 1.1) with some extra features and more support (like TRIM). The reason I upgraded was simply because I got an SSD and wanted TRIM support.
I will probably hold out, like I did with Vista, until I need an OS to support something I am trying to do or have been proven to provide better performance in game.
I read an article can't, remember where now (maybe PC Perspective or Hard OCP), where they benched a number of contemporary games. The performance was usually on par or slightly better in Windows 8. They also commented that on a more subjective note that the Windows 8 experience seemed smoother than Windows 7 due to the phenomena of "micro stuttering" that has been present in pretty much every OS up until now.
That said I myself don't like the new interface or the step backwards that MicroSoft has taken in regards to an open platform. Not that Windows has ever been open source, but it's always taken a hands off approach with developers. With Windows 8 they seem to be moving towards a mandatory certification process for software, somewhat like Apple's model. I honestly think this approach will stifle innovation and creative thinking.