upgrading from Q6600 to 2500k seems to be the standard move for most gamers at the moment
I personally would upgrade, and did, but for me that was because I knew I could afford to and wouldn't have been satisfied unless I did so.
As for that last little spec you done with the Corsair case, it's a great little set up there. The stock cooler can be pushed to about 4Ghz so they say, but even something basic like a AC Freezer 7 Pro for £20 should perform a little better, but if you do that you might as well go for a gelid tranquillo.
My advice would be get a 60GB SSD instead for now to load windows and a few games/programmes on. And put the rest towards a decent cooler that will look nice inside that beautiful case.