I use
Powerstrip
You raise the core and memory 5mhz or so at a time and run 3dmark2001 and look for artifacts or lockups... If you get artifacts, back down the core or memory until you find a stable speed.
There is no way anyone can tell you how well your card will overclock, some people can get over 300/300 while others that have retail cards cant go over 285/285ish even with better GPU coolers and ramsinks.
Ps the ATI heatsink is a piece of garbage and I recommend using a Crystal orb affixed with Arctic Alumina Adhesive. Ramsinks may or may not help you, I suggest while your running 3dmark2001 place your finger on a memory wafer and see if its hot to the touch, if it is Ramsinks may be a wise investment and may help you get a few more mhz.....