nobody is going to agree with your logic at all. and your cpu WILL limit a gtx480 right from the get go at 1360x768. in more cpu intensive games you will give up 50% of what a gtx480 can do at that silly low resolution. I hate to be rude but what you are doing is extremely stupid. a 6850 will give you the same playable framerates at that low res and then in a couple of years you can upgrade to a better gpu if you want to. heck even the 6850 will not come close to being fully utilized in more cpu intensive games at just 1360x768 with your cpu. in 2 years or so even a $90 card will give you the same performance as a 6850 does now. my way is cheaper, uses less power, and gives you the same playable experience while allowing you to keep up with newer card features.
I do understand what your saying. You are talking to a guy that bought a 1200 watt psu for a gtx470 or gtx480 and a dual core processor. Logic doesn't really apply to people on this forum...especially when it comes to what you really "need" in terms of hardware for what you are doing. Realistically all you really need is a 5770 and you got a great gaming experience. I do not want to have to upgrade the gpu every refresh. If I can get a good deal on a gtx480, say $300ish or so, and it lasts me 5 years, that's great. Heck maybe it will fail on me, and the gtx480 will be EOL in four years, and they will have to replace it with a new gen equivalent card, lol.
But looking at reviews, at lower resolutions the GTX480 gets about a 60-80fps advantage at times over a 5870. I've noticed from reviews that the GTX480 actually does well at lower resolutions, and that ATI kind of does better at higher resolutions. I like lower resolutions because I get more fps and smoother framerates, usually it will stay above 60fps even in the most demanding of games. Plus to stress the gpu more, I can always just apply more AA/more eye candy.