Q6600 to 1055T for gaming is not really an upgrade at all. Basically a step sideways. AMD clock for clock is slightly slower than Core2 and no games use 6 cores. If you were using it for video/photo editing I would say the 6 cores would be an advantage but the Thuban is not a great gaming CPU. X4 955/965 are better chioces but still not much of an upgrade especially if the Q6600 is overclocked to 3.2/3.4 range.
Yup, ^ +1. Get a GTX 480 & upgrade your PSU to a 650 watt one (if you're not looking to SLI). With an OC'ed q6660, it'll pretty much annihilate that proposed AMD system of your's.
Then next year, as both AMD & Intel come out with their new platforms, just upgrade to that with your still new GPU & PSU. For $1000 builds, it makes no sense to to me to buy right now. If you wait, you'll get newer tech at same-ish prices, or the 1156/1366/AM3 stuff at lower prices.
This will be a very good gaming system. Just two things though -
1. If your resolution ain't 1920 X 1080, you might not need the 480 for now. A 460/470 will do just fine. Having said that though, next year when you change the rest of your system, you won't need to invest in a new gfx card or a PSU. So might as well invest in a nice 22"/24" full HD monitor
2. If you have SLI in mind, (with OC'ing) you might seriously consider a 1000 Watt PSU (1000 A on the 12 V Rails should do it).