Last I checked Nivida SLI in linux only supports 2 GPU's and windows supports all 3.. to power one monitor.. also try enabling composite graphics and spanning 3 or more monitors across multiple GPU's in linux. It's been broken since Ubuntu Hardy, and the only way to get it to work is to use an outdated Xserver-XGL to do it.. Xinerama is not the answer because it also disables composite..
We have several clients that had to choose windows because they had 3 or more monitors.. Linux just can't do it right.
With fglrx, you can do that with 3 monitors on shipping cards and up to six with future cards. It's one surface with RANDR viewports over it, so composite does work.
Originally Posted by d2globalinc
However, lots of apps get very confused about the "fullscreen" and mixture of xinerama and randr information. This makes compiz not quite the experience you'd expect.
Yah - the eyefinity stuff might save the day with a 6 port card, but I was unable to get 2 3port eyefinity cards to work correctly under ubuntu Karmic..
This has been the best we've accomplished:
thread and info here: