I bought my computer yesterday and this is really odd.
When I installed the new ATI driver (Catalyst 10.2) my monitor, which is a Samsung TV, says it doesn't support this mode. I have tested the display on my friends monitor and it works perfectly but for some reason it doesn't work on my monitor.
So at the moment my pc doesn't recognise the GPU as an ATI 5859 but as a Standard VGA Graphics adapter, so i can't do much on my pc.
I have also tried running on the same screen resolution as was supported before I installed the Catalyst but my monitor still says that it doesn't support this mode.