Currently I run two monitors and have two different graphics cards in my machine(no sli), I have each monitor plugged into a different card but I came across the thought today that it is possible that the primary card is doing all of the rendering and the second card is just acting as a glorified buffer minus PhysX (which is fine). Then should I plug my secondary monitor into the primary graphics card to skip this step? Anyone know how rendering is assigned within windows?
I am 90% sure that for gaming at least the primary graphics adapter is all that is used. In order to use both cards you would need to SLI them together. For CUDA applications you can use both cards, which is the default method, or assign just one card for CUDA use. You can also assign a second card to be just PhysX in games if you want in the Nvidia control panel.