I'd try to get your 260 working on your current setup before going i7. Personally, I don't think i7 is worth the money at the moment. Post up a screenshot of your GPU-Z. The P5B has a reputation of running the PCI-E lane at 1x for no reason.
I have gamed with an E8500 @ 4.6ghz, Q9650 @ 4.4ghz, and now am back to an E6750 @ 3.8ghz and there's really no noticeable difference at all between any of the setups.
I've also got an E7200 coming today