I understand the logic of staying with one card,it makes sense for money/temps/and psu requirements,aswell as the increased noise.
I wouldnt personally consider a 570,as clearly your not afraid to overclock your gpu's and i understand those cards can have issues with vrm's...
how about the evga 460x2win?
The 480 would get my vote,reasonably quiet but well powerful.
Is there a reason why you arent considering amd for gpu's?I understand they are alot cheaper an quiter.