It's not that bad to be honest, it's nothing like halving your framerate. Bear in mind, it isn't rendering two screens, just two views. The actual screen size is on par with a single monitor. The catch is that it's way more important to keep your framerate high because as soon as you lose low persistence, it's very noticeable and much more likely to induce nausea.
I think there's a bit more substance to the claims on this iteration, particularly with regard to the memory. But either way, with VR SLI a pair of discounted 9 series cards could also be a great choice.
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