Looking at a few old listings on Newegg of deactivated items ( http://www.google.com/search?hl=en&as_q=nForce+650i+Ultra&as_epq=&as_oq= &as_eq=&num=10&lr=&as_filetype=&ft=i&as_sitesearch =www.newegg.com&as_qdr=all&as_rights=&as_occt=any& cr=&as_nlo=&as_nhi=&safe=images )

it looks like the hardware should support 8gb of ram, and as previously mentioned, the manufacturer propably put the 4gb limit due to OS constraints. Also, looking at the tech specs for that chipset ( http://www.nvidia.com/page/nforce_600i_tech_specs.html ) be sure to use DDR2-800, don't buy anything fancy here.

That said, DDR@-800 is cheap, Windows 7 is even cheaper.

Also, to emphasize previous points, full HDDs don't play nice, I'd consider another HDD for my WoW, a small SSD would be nice and would return some space back to your porn errr family phote storage.

Moving down the list, your 8800GTS 640mb DOES NOT have the G92 processor, it just missed that boat. An upgrade to even a 260 would be monumental.

Even further down that list are your mobo and processor; while great 2 years ago, they are hardly cutting edge anymore. You should be able to squeeze more frequency out of your overclock, or possibly drop in a Q9550 But if you are nodding your head down this entire list, and you can justify the cost thus far, might want to start thinking i7...