The problem is the Mac minis hardware. I have the same issue with a FullHD screen.
Due the tollerance of the display VGA works better, but DVI turns the display into a flickering hell.
The problem is the build in radeon chip which wasn´t developed for such high resolutions/frequences. I even can reproduce the effect with OSX. When using OSX itis just not that often, as Apple may used some more finetuned values to setup the resolution.
Geit
