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They should of used the 790i.
It's clear that NVIDIA has really got its dual GPU SLI technology sorted out, but when you start mixing it up with three or four GPUs the performance increase while present, is very small, especially in relation to what it costs you to go down that route.
The GX2 continues to be a good offering for people who want to jump on the SLI bandwagon without getting themselves a SLI motherboard. However, if you're looking at building a new system it might be worth checking out a 780i motherboard and a pair of 9800 GTX cards which really gets things pumping.
NVIDIA has been seen to put a lot of effort into the SLI driver as of late, but it seems that most of the energy has gone into getting two cards to run extremely well together as opposed to three or four.
They should of used the 790i.