ATi Radeon 9600xt Overclock?

Hey,

I just got an ATi Radeon 9600xt 256mb.

I want to overclock it and I downloaded Rage3D Tweak v3.9, The stock clock on the card is core=499.50 memory=297.00. I don't have any experience overclocking video cards and need some suggestions on where to go from here.
Is this a good OverClocking utility (Rage3d Tweak)??
What should I bump up memory or core, or both??? and by how much before the stock heatsink and fan isn't enough????

The 9600XT is very close to its limits already because it is just a higher clocked 9600,9600pro.

The best I could do was 526/330.