bcavnaugh
For another test you can connect your Graphics Video Cable to the second card as well.
You can do this with the Power on to allow the NVIDIA Control Panel/Driver know.
Then the Bottom Card will become the Primary and the Top Card will become the Secondary.
Some Games that do not really support SLI your second card will just sit their doing nothing.

This was very important and helped me figure out the differences between the two GPUs, without having to mess with the hardware:
-The top GPU has a boost 35 Mhz larger than the bottom GPU. (Default settings)
-The bottom GPU is actually a little warmer (2-4C).
-In SLI, the card connected to the monitor is 80% -95% of usage. The other is at 99% almost always.
 
Using Precision, I added + 51Mhz on the bottom GPU only, and with that, both voltage equaled 1,043.
The clocks are stable at 2025Mhz now (I do not need much OC). Never drops.
The only question that remains is why the primary GPU (Top) does not have its usage as the secondary GPU (Bottom), on SLI?  :-/
 
Cheers!