Yes and No 8800 GT better then g80 8800 GTS (320/640 mb), a little slower then the g92 8800 GTS (512). But has a better cost to performance ratio then both because g92 gts does not really give you a performance advantage, way to close. And GTX is a dead card for new buyers.
People will disagree with me on your psu I know it. 600 watt perfectly fine.
New C2D cpu's are power efficient in relation to there older cousins, P4 and Pentium D. The 8800 GT and new ATI products are more power efficient then previous generation cards as well. Power needs are and need to go down. That said their are people on here and out their that insist on really high watt PSU's even though power draws on modern system's are droping and will continue to do so for the foreseeable future. People simplify it by adding up wattage of your components and then say you need that much. But if you look at this site's and other's review's you will see that power draws are not what the wattage adds up to under full load. All systems including ones configured in sli with extreme series cpu's pull way lower wattage then what you would get from adding up the wattage of the part's. 265-400 watts for ulta powerful systems with 1000 watt PSU. That said there is a average of 20% inefficiency to be added on as well. What is more important then wattage is 12 and 5 volt circuits. You need two 12 v minimum, three would be fine though, and that 600 watt would do that for you.
I have a 2 year old Dell fully upgraded, Pentium D930 3.0 ghz, 2 gb 6400 ram, 2 hard drive's , 8800 gt. I have 375 watt PSU, under rated really push's 450, 2x12 volt rails. At wall Tower only, in game system maxed (250-285 watts). Your proposed parts would be fine in sli overclocked with 600 watt system. In a few years 550 watts will be fine for all out systems.
High efficiecny PSU'S better, less waste and quailty parts, if it's in your budget.
Crazy, Wasteful PSU's and computer's are one of the millions of symptom's of a wasteful society.
Perfect for your system
http://www.antec.com/us/productDetails.php?ProdID=28550
Look at the system config, then look at power consumption, that is the full system! This will also give you info on cards you want.
http://www.techspot.com/review/79-geforce-8800-gts-512/page11.html
http://www.techspot.com/review/79-geforce-8800-gts-512/page2.html