I dont know if 2 cards makes much difference really, I was using 2 x GTX285's for quite awhile and didnt have to change anything compared to one of them or the GTX295 I use now. Always same vIOH (1.13v BIOS giving 1.11v real) and stock PCI-E voltage, only things I ever increased were Vtt and Vcore and I had 4500 MHz stable.