Comment 9 for bug 298094

Notice how the h/v rates don't match the vendor's advertised capabilities:

Via EDID:
 HorizSync 31-65
 VertRefresh 58-62

Via DDC:
 monitorrange: 31-65, 58-62

Xorg.0.log (radeonhd):
  (II) RADEONHD(0): Ranges: V min: 58 V max: 62 Hz, H min: 31 H max: 65 kHz, PixClock max 110 MHz

Advertised specifications:
  * Frequency Fh:29-82kHz, Fv:55-86Hz

So, what happens if you plug in these values into your xorg.conf?

Section "Monitor"
    ...
    HorizSync 29 - 82
    VertRefresh 55 - 86
EndSection