@ methixOr: What's your monitor resolution? It's unlikely you'll see much improvement over a HD 6870 if you're playing at 1280x1024. Also, what games are you playing? If you're a big fan of RTS games then it's very unlikely a faster graphics card will be a very cost effective upgrade.
I doubt you'll get any 'bottleneck' issues the i5750 is a pretty quick CPU and you can always crank up the eye candy to slow down the 7950;).
BTW aftermarket coolers are cool! I suggest you look into the subject, even a cheap Hyper 212 Plus, like mine can easily cope with an i5 750 at 3.4 GHz without drama.