EX9 performance = GPU?

hi all!

Q6600 @ 3,4GHz
4GB DDR2 800MHz
Geforce FX500 (8800 GTX is in my new pc)

i do videotracking with two webcams @ 30fps, 320x240
each of them:
contour with cleanse
grouped with other objects in a renderer @ 320x240
pipette @ 160x80

i get 60fps
if i go for a 320x240 pipette, i get around 20fps

the renderer and the pipette are EX9 nodes.
so does the GPU slow down my patch?
my CPU load is 45%max. none of the cores over 60%