I've just finished reading the Nvidia FAQ on multi-display and SLI, and I simply needed a little more info on the subject.
Here's what they say:
How many monitors are supported when running in SLI mode?
With GeForce R180 drivers (or later), standard SLI configurations for 2-way, 3-Way, and quad SLI support a maximum of two monitors. Additional monitors (up to 6 monitors total enabled) may be enabled by using either a motherboard GPU and/or a PhysX capable graphics card (GeForce 8 series or higher with at least 256MB of memory) that does not have the same GPU as those that are SLI enabled. More information regarding multi-monitor in SLI can be found
So if I understand correctly, if I want to profit from the extra performance of SLI 480s, I can only plug 2 monitors in the master 480. If I'd want a third screen and still have SLI enabled(?), I would have to add a third GPU, different than the SLI 480s (ex 9800 GTX), and plug that monitor on the 9800 GTX.
As soon as I plug a third monitor on the SLI 480s, what exactly happens?..