yeah you have nothing to worry about. Sandy Bridge would be a little bit faster in some cases but no reason to upgrade. just wait a year until Ivy Bridge comes out and/or you want the next big gpu upgrade.Ooops, the resolution is 1920x1200.
I doubt there would be a significant jump in performance at 1920 from your CPU @ 3.6 to a Sandy Bridge, definitely not much. I have a 560Ti on a Q6700 @ 3.3 (so you are way ahead of me) and it was a huge improvement from the GTX 280 I had before. CPU intensive games like Civ 5, SC2 and other RTS might see a jump but I don't play those (only FPS, racing and RPG).