With my CT2A machine (25MHz Bus, 50MHz Videl) using centvidel I'm able to get 1600x928x256 at 28Hz refresh rate on the U2410. The monitor thinks it's 1600x1000@28Hz, the picture is almost perfect after manually adjusting the "Phase" value to something around 90. Setting aspect ratio to 1:1, the picture is smaller but pixel-accurate.
Now to scale my background image accordingly...
Even 1888x912x256 at 24Hz will be displayed, but there the quality is bad as the monitor thinks it's 1280x960 and doesn't sample all horizontal pixels.
Schneider CPC464 (long retired), Atari Mega ST4 (retired), Falcon+CT2A, Falcon+CT63+CTPCI+Radeon 9250, Milan040+SCSI+Rage