Section "Device" Identifier "Configured Video Device" Driver "radeon" Option "NoAccel" "true" Option "UseFBDev" "true" EndSection
The result... OMG... I have native resolution again... I can't believe I didn't think about trying that, but I'll be the first to admit I've been stabbing in the dark...
So what next, the issue is now totally reproducible - NoAccell fixes it... I'd like to get a fully functional card back.
Thanks to everyone who has chimed in here!