Strange, I can set the clocks for my two 5870s with aticonfig that are outside the 'Configurable Peak Range'. Might have something to do with the fact that I flashed their bios with already altered clocks (to 920/354). In my case aticonfig reports the range as 600-900 for gpu and 354-1300 for memory, but I'm running them at 950/200 (set with aticonfig). Maybe it's because both clocks set in the bios are already outside of aticonfig's range.

I would use AMDOverdriveCtrl, but my rig is in the basement, without a monitor, keyboard or mouse, so I only control it over ssh. Guess I should have set up a vnc server while I had a monitor still attached .