9800 gx2 quad sli or 4870 x2

Hard to say without knowing the specs on your whole system. Big question would be whether your system will bottle neck multiple 9800GX2's or not.

Tough call.

If it was me and my psu had the power and connectors I would go with another 9800 gx2.

I'd justify it like this:
gx2 costs $300: Spend $300 more and get more power.
4870x2 costs $900: Throw out previous $400 investment and add $500 for a new card.

But if I had no money problems and bang for buck wasn't important then I'd grab the 4870x2 and hope that by the time I can buy the 2nd 4870x2 there isn't another cool gpu out that I want instead.

There are some other slight differences which probably dont' matter so much:
-------
9800gx2:

DX10
Shader Model 4.0
AA 16x

-------
4870x2:

DX10.1
Shader Model 4.1
AA 24x

On my planet the HD 4870X2 costs around $530, not $900.

A GTX 280 would actually be less satisfying than a 9800GX2. I remember when the GTX 280 came out we were all reading reviews and comparing with the 9800GX2 and the disappointment was huge.

Give us the specs (case, MB, PSU, CPU). Also, what are your favorite games? Some games (like Crysis) favor nVidia cards, while others (like CoD) do a fantastic job of scaling in Crossfire.

what about 260 x 2?

"Also note, the 9800GX2 can not Quad SLI under XP (NVIDIA was afraid of the cards eating too much RAM from the system i guess...) "
http://www.tomshardware.co.uk/foru [...] ise-needed

So I guess unless you're using Vista then it'd have to be the 4870x2.

Here are some very high fps with dual 9800gx2s running Crysis on an OC'd setup:
http://www.freeimagehosting.net/uploads/c92b1ceaf6.jpg
http://www.tomshardware.co.uk/foru [...] uad-280gtx