Originally posted by: nRollo
You and Taltemir are both right.
In the main body of my post I was only thinking of 3870X2 vs single GPU, in the edit I added later I was thinking of 3870X2 vs GX2 and how the GX2 s multicard limitations are lessened by the additional driver flexibility. The GX2 would still have some multi-card limitations though, so a single card offering similar performance to it would be "better" and/or worth more money.
I see this as the main problem with R6XX and ATi's stance from the beginning that multi GPU is how they would combat the 8800U and 8800GTX. Multi GPU has inherent limitations, more so with Crossfire, even though they've come light years from where it was just last year.
To me there are two reasons to go multiGPU.
Best: To get a level of performance unavailable with single cards, and for this you accept there will be variable scaling, more tweaking, more expensive hardware.
Second: You can't afford that level of performance, but realize adding a second card down the road you pick up used or discounted may be cheaper than selling your old card at big loss, buying new high end at launch price. (in short- flexibility)
A single 3870X2 doesn't offer consistently (appreciably) higher performance than a 8800U or OCd GTX, so it's more a hobbyists solution. An interesting alternative.
This of course may all change when the drivers for Quadfire launch as the one set of benches I've seen offer good scaling, at which point it may be a more attractive high end dual card solution.
My $.02