The better upgrade ?

[COD4000]

Hi there, my current PC specs are:

Phenom II 940 @ 3.5ghz.
4 gig DDR2 Ram.
Asus M3A79-T.
Ati 5870.
X-Fi Extreme Gamer.
Corsair HX 750W.

Would I see a bigger increase in performance upgrading to Sandy bridge and overclocking it, or upgrading my 5870 to a 580. I can play most games alright, except for GTAIV where I can get some pretty bad slowdowns and in Crysis i can get the odd slowdown and stutter.

 

[CAT-THE-FIFTH]

What resolution are your playing at BTW?

What operating system are you using?

Your system is fine IMHO and don't get caught up into all the hype. AMD Bulldozer is being released in Q2 2011 too(around April supposedly).

Also,Crysis should run fine on that setup and I would make sure that your drivers are properly installed,your hard disk is defragmented and any unnecessary software is uninstalled.