2nd (better) Video Card placement
 

I bought a NVIDIA GeForce 8800 GT to supplement my installed NVIDIA GeForce 7300 GT video card. One card will run two Samsung LCD's and the card other a third similar monitor. Would I see any improved performance in programs such as Motion if I swap cards, putting the 8800 in the main spot (running 2 monitors)? Or does the computer utilize both cards for improved realtime rendering regardless of what slot their in.

Thanks.

MacPro 2 X 2.66 GHz Dual-Core Intel Xeon - OS X.5.5 - 9 GB RAM