First of all, a single 280 is already overkill for most stuff.

A duo of 280s will increase your horsepower, yes, but the end result isn't twice the frame rates, in fact it isn't even 50% extra frames compared to a single 280.

What people are saying is that if you have, say, 400$, it makes more sense to spend 200$ now, then keep the other 200$ to spend in two years time for a brand new card to replace it. Because that way you WILL get more than twice the frame rates. It makes more financial and practical sense. Besides the fact that a duo of cards (SLI) has a couple extra technical details that are an arse to deal with, going with single cards is simply easier.

Also, please check your PSU. You're already going to need a good one for a 260/280, and ONE HELL of a good one if you're going with a duo of cards. Plus a duo of cards would have ridiculous power consumption, take a good look at the electricity bills.

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