An E5700 is already a pretty good match for a 4770. I assume you will see a bit of an increase, but honestly you would have been better off just overclocking the E5700 and spending that money on a newer GPU and CPU cooler.
Yes I know, I used the E5700 in another Pc which cpu and motherboard were damaged (a storm fried my pc, modem, even the speakers....).
So I decided to update my rig...
I read the Tomshardare "Best Cpu for the money " guide, so I decided to go for the i3 2100... Although I´m concerned about it only having 2 cores.... (I´ve another post talking about this...)