If you're willing to spend $450 on a new graphics card, a cpu upgrade is in probably order as well. For $300 or so a new p67 mobo + i5 2500k would be a great match. I wouldn't go for an i7 as they tend to perform very close than the 2500k in gaming (toms says so in their monthly gaming cpu reviews) but are significantly more expensive.
I enjoy gaming on my 5750 at 1080p with moderately demanding titles (dirt 3, skyrim) but upgrading from my old athlon to a 2500k was the best decision I've ever made. Games do perform slightly better, and I'm sure you'd notice a much greater increase with such a powerful card. For me, coming from such a crappy dual-core athlon, regular app performance was huge as well. For you maybe not so much, but a single fast core is often better than many slower parallel cores and I think that could give you some great performance benefits as well.