Did you miss the part where the OP is running 3D? He's said it multiple times, and that's where he's lacking performance. 3D puts twice the graphics load on the GPU - a much higher hit than raising the resolution an notch or using AA.
He would see scaling with a third GPU.
Prescisely - I was happy as a clam even at 2560x1440 (!) in "plain 3d" as far as FPS, then I went "down" to the 23" 120hz 1080p panel, and got the shutter glasses, and FPS somewhat went to hell when I added the Stereo3D.
nVidia lists single boards in the 2xx-series as suitable for this technology? Those must've been hard times.
CPU utilization graphs show me no maxed cores for any substantial time, 30-60% avg utilization across up to 3 cores, depending on the game.