I think your going to spend a bunch of bucks and not get much.
920>3570......there will be a bump in cpu perf....as to how that will xlate to some game.....unknown.
I doubt it will much.
W7>W8......No......Let the dust settle with W8.
Get enough ram that the swap file stays quiet while your gaming.
If your games are hammering your HD for data......think about a SSD or a hybrid.
Need advice on whether or not I should upgrade my rig. It has served me well for the past 3.5 years. I plan to upgrade the following components as my 670 gtx is perfectly fine:
i7 920 ===> i5 3570k
ASUS P6T ===> ASUS P8Z77-V PRO
Windows 7 premium 64 ===> Windows 8
Do you think there is a need right now if my primary purpose is gaming (Planetside 2 for example)? My i7 920 is stock and overclocking on air is not an option where I live especially during summer.