Prophecy

From what I've read:

The 9800 GX2 is $600.
The 8800 GT is $200.
The 9800 GX2 has the same performance as 2 x 8800 GTs running in SLI. ($400)

I wouldn't think about buying a 9800 GX2 yet. No clue about your second question.

However, below are a few reviews of the 9800 GX2:

Early Test

Overclocked and Tested

with ForceWare 174.51

Running in Quad SLI

Edit: Off hand anyone know how much power two 8800 GTs in SLI need vs one 9800 GX2? If you have to buy a new expensive PSU, it might all come out in the wash.

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E Potete Raccogliere Le Ricompense.