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2 x 290's better option if you really need that much power and cheaper than 3 x 280's.
Why 3?
Also, which MSI Z87? You'll have more luck with an XPower than a G45 Gaming.
I see. Howabout the fans on 290s? I thought they were quite noisy?
Hmm Im conscience that the 290 power consumption is 419watts, according to the review.
I have an 850W PSU so Im not sure two of these are going to work with my PSU...