I just ran ATITool 0.25 Beta 14, and it showed that the X1600 in my low-end iMac was running at 313MHz core, 300MHz memory. So I overclocked it. It's now stable at (no typo) 440MHz core, 576MHz memory. Yes, that is about 50% faster, and FPS readings back that up. Keep in mind that the Mobility X1600 is supposed to be clocked around 470MHz core, 470MHz memory. The desktop version of the chip is the same, but is clocked about 100MHz+ faster. It should be able to be pushed even faster when we actually have the fans running properly.