Yes, you will see a pretty significant upgrade in performance. If your mobo can support the q6600, you will be set for at lest a year or more for gaming. And I am guessing you are going for a 768MB 460GTX? That will be a good match for the q6600.
Also make sure the your PSU can handle the load, you are going to put close to an extra 100W at load on it, I would recommend a solid 450W PSU at least here.
If your CPU is significantly weaker, you might consider a lower wattage GPU, like a 5770.