OK, installed the 8800 in slot 1, moved the 7300 to slot 4.
In WoW with my old 7300 (everything maxed but ground clutter and full screen glow OFF) I got between 20-40fps most of the time with spikes as high as the mid 80's.
With the 8800 with the same settings, I get slightly more FPS. More like 30-45, with spikes as high as 117. However, if I turn on the full screen glow, it doesn't drop my frame rate in half. In fact, it doesn't drop it at all.
So, for me I am getting 30-45fps most of the time and the game looks MUCH better.