The gpu would give you the bigger performance increase. The x4 965 might bottleneck the gtx 670 but only a little.
Thanks for the quick response, although people have told me that ARMA and WarZ are more CPU intensive and that my CPU is the reason that I am getting poor FPS. Would the Video Card still give me improvement in these games?
I've decided to go with the 670 for now. I'll be getting the i5 in January anyway so it's not too much of a problem. As for the overclocking, I'll check around the forums here and maybe do a minor overclock because I only have the stock heatsink.
Thanks for your help.