Not claiming that you are saying isn't true, but I had a opposite experience. My 2500K with two active cores was giving me better experience compared to my Phenom II X6 both running a 7950. I'll launch the game tonight to compare the two systems again to see if anything has changed with the recent patches.
The i5? Do you mean with the 7770? Thats easy enough to do. Just get cheaper case and you probably can find a cheaper HDD around also.
HardOCP determined the 7770 to have the same playability experience as a GTX 560 Ti. The performance isn't as good, but its a decent card. Especially if you are running a resolution lower than 1920x1080.