For those not aware of it, the Atari PTC1426 has a switch on the back of the monitor that toggles it from standard VGA mode to TT compatible VGA mode. So the difference can't to huge if Atari itself manage to put it all in one monitor. As we all know they did a lot things on the cheap. ;-))
Might be worth while to find the PTC1426 schematics and see just what this switch does.