I love my Q6600. It's running at 3GHz w/ a cheap aftermarket air cooler. I was too lazy to toss my Thermalright Ultra 120 on it so I went with a cooler that didn't require a backing plate. Along that line of thought, if you do want to overclock, buy the heatsink/fan now. Most of the good ones require a backing plate because of their weight.
As for the video card, I would be tempted to back down to the 4870 (I just with they would up the memory to 1GB) and spend some of the leftover cash on a good heatsink/fan and maybe bump the hard drive up to that 1TB drive that beats the old Raptors (or if that's overkill, seagate or samsung makes a 640GB w/ 2 320gb platters that is supposedly on par with the 1tb drive and is on sale for less than $100).
No matter what, it sounds like you have a great setup.