Wait wait, so, 8800gt for about £140, 2 of them for £280, comaped to £300 for a 8800gtx. Where a single 8800gt is within 20% of the performance of a 8800gtx.
So, lets say we add 40% boost for SLI. its going to beat the 8800gtx isnt it, by theoretically 20% with that boost. For £20 less. And let's face it games like crysis UT3 bioshock none of them are going to give just a 40% boost from SLI once the drivers are all sorted. SLI shows better under rmoe strain too so when you're in the 20 - 40fps area theres usually a better % boost then when your in the 60 - 70fps area, Ill see if I can find the review I saw of that.
But with the price of this new 8800gt and its performance theres no reason to not go SLI, 2x 8800GT's and you can kiss the 8800GTX goodbye..
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Imo SLI isnt a waste aslong as you use it right, its great for smoothing out those min framerates when playing a game even if the max doesnt go up by tons.
The whole 20% to 80% thing is true yes, but not for the newer games, all games starting to come out now after nvidia gets their drivers in gear have shown great boosts in SLI, its just mainly older games that dont like it that much.
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Aside from all taht its good for upgrading, say one high end card rom next gen is 2x one high end card from this gen, well you can buy thsi gen's high end card, tehn when next one comes out, simply purchase another one of your cards to get simular performance. Rather hten buying a new £300 high end then it costs like £150.