James,
your pc is very strong on some points, also very weak on others.
Your PSU is a very potent one, designed to run multiple high-end cards in SLI/Crossfire along with an overclocked i7 cpu.
Your CPU is an aging one, a bit slow nowadays, but still enough not to limit most of the vido cards on the market. Btw which socket your mobo has?
The RAM is pretty much enough for any CPU you can put into you mobo (you have it in 3 sticks, right?). It would be near useless to upgrade it.
That 9600 gt is an aging card, but can run AH maxed out except the self-shadowing. The gtx 550 (for those 550 bucks) will be able to set the shadows to 4096, but no more.
Btw the ram on it: the ones equipped with 2GB rams hav the old ddr3. The 1GB ones have the much faster ddr5, so the smaller is the faster in this case. I would choose the ddr5 ones, or better, switch to the amd/ati and get a hd6790/6850 for about the same price. (as an alternate, i got my older ati 5830 for 130 bux. cheap, fast, but eats 170 watts... not a good choice) But if you dont play anything else totally maxed out but AH, that 9600gt still can serve you for a while, til the prices get pushed down.