I´m running two 280GTX in SLI on an ASRock x58 Deluxe3, played a little around with GPU-Z to see what temperatures i was getting. I noticed that it shows my primary GPU as GPU 2, the same is true for for Real Temp.
My screen is connected to the top card and i am seeing bios upon start up and everything.
More aboutprimary showed
If everything works fine it shouldn't be a problem, but take not which PCI-E slot is master and hook your monitors into that.
Th primary is usually the card closest to the CPU
The card that my monitor is connected to is the one closest to the CPU. As said i can see my computer post on screen and everything upon boot.
But still it shows my primamy GPU as GPU 2, even shows it having most of the work load and such.