enigmatic fps

Hello
I’m observing interesting effect in OpenGL.
I render rather heavy animation scene with about 50 models
and scetches (all with automatic 0), plus 1 grab 640 480.
Basically when I start qmetro 40, I get 22.5 fps. Then
when grab and all the animation math starts, the rate goes
down to 12-15.
But few unpredictable times render starts with fps exactly
25, and it does not slow down, when I switch on grab and
animation. Then the whole scene goes smooth and much
easier to control.
I tried to restart MAX/MSP and system, but still could not
find any method to get certainly this "smooth" 25 fps
rendering…
May be somebody can suggest, where I should search for
solution? May be graphic board settings?
Or isn’t there in MAX certain tools to control OpenGL
performance?
Thanks
Alex

MAX 5.0
VISTA HOME PREMIUM
OS VERSION 6.0.6000
INTEL(r) CORE(tm)2 DUO CPU T9300 @ 2.5 GHz 2493 MHz
Realtek High Definition Audio
NVIDIA GeForce 8600M GT