@Layback Bear
The driver was designed for both cards.
The driver was installed on both cards.
I believe if you ran 2 of the same cards they would act normally you would not be getting the extra power SLI offers though.

@Dude
I'm going to try removing the 550ti later today and will just try the 660 for both monitors but I have a new problem surfacing now the gtx 660 keeps crashing now. My computer will lock up for about 10-20sec and then the screen will go black, recover and then tell me my Nvidia driver stopped and recovered. I also noticed this event in the Event Viewer.
"The description for Event ID 14 from source nvlddmkm cannot be found. Either the component that raises this event is not installed on your local computer or the installation is corrupted. You can install or repair the component on the local computer. If the even originated on another computer, the display information had to be saved with the event. The following information was included with the event: \Devicec\Video9 !06d7(2648)
Now I have seen \Video13 before to any clue to what this could mean?