overclocking nvidia 9600gt for laptop

Hello, I noticed that when installing powerstrip for my HP Pavillion
dv5 notebook, with gpu 9600gt [512mb], 4gb ram and win 7 ultimate,
that I am able to overclock the engine and memory clocks. At default,
they are both at 400mhz, and I am wanting to overclock them in order
to notice a slight performance increase when playing high end pc
games, such as Grand Theft Auto 4. Now I realize the consequences for
overclocking a laptop gpu, so I am asking if anybody knows what level
I should overclock my engine and mem clock to. The interesting part
is
that at default, they are both at 400mhz - perhaps that is because it
is a laptop. At whatever level I increase the clocks mhz level at,
should it be equal in this case. Help is much appreciated.
Thank you