My computer is used for gaming CODMW2, BFBC2, Splinter Cell: Conviction.. ect. and also I am study computer networking in school, then I am starting to get into Photoshop, Dreamweaver,Flash CS4 ect.....
Now, being a geek I know that newer tech is a lot of times better but not always, but I want to get others options.
For gaming you will see really no real performance gains Your best bet would be just to overclock the Q6600 as far as you can get it until something really worth the upgrade comes around. Rite now your Q6600 and the GTX260 is still a great gaming rig I personally would wait or if you really want to upgrade spend the money on a HD 5870 first then think about upgrading the rest of your platform.
With a decent OC on that Q6600 you will still get to max out most games with very playable framrates.
Gaming-wise, you'll probably only notice few frame rates higher, that money would be better spent in GPU if your worry is frame rates, however, if you do CPU intensive work, such as 3d Rendering or video editing, you'll probably notice almost 2x gain in performance.
I used to own a Q6600 OC'd to 3.2ghz, compared to my new X6 1090T OC'd to 4.2ghz my render times are cut to half! now thats a performance boost.