[Help] What's best for my machine....

My system config : E8400 @4.2 ghz, 2x2gb pc8000, Biostar Tp35-d2a7 (p35 chipset), Silverstone Olympia 700W

Considering upgrade my current GPU - 8800GTX 768mb (g80)
Any suggestion on upgrading? I play at 1680x1080 (22" )

Consideration : - Single card (since my mobo doesn't support sli or x-fire)
- Nvidia / Ati, no problem

So i need your opinion guys, what's the best vga for my system, i mean the most optimal combination, so my vga doesn't get bottlenecked from my cpu, and vice versa.

Thx in advance

PS: my personal consideration: (is it too high???)
- 4850x2 (Pro: fair price.... Cons: Ati Driver a little bit, noisy, heat, high power consumption)
- 280gtx (Pro: Nvidia driver.... Cons: Fear that GPU backplate wont fit in my mobo, ram slot is too close too pci-e)
- 285gtx (Pro: Same as above .... Cons: Price/performance compare with 2 card above)

A 4850X2 or a 4970 is not going to be much of an upgrade over what you have now for the money you are going to spend.
You'll need to at least go 4870X2, or a GTX285 I would think to see enough benefit to make it worthwhile.