In my experience my 1.42GHz mini doesn't like 1920x1080 (FullHD) displays via DVI either. I've tried it with 3-4 displays and a video projector. According the talks I've also got the impression that other 32MB minis are problematic too, but it's been said that you would have better chances with VGA which I haven't tried in the degree to make conclusions.

But OTOH, my 1.5GHz mini (64MB) has worked just fine on the same displays via DVI, so I think there's something different in the hardware between the very latest model and others. I have my 1.5GHz mini in everyday use in FullHD monitor and it has worked even on FullHD video projector etc.

But your observation about 1920x1200 is funny indeed. One would have thought that going bigger resolution wouldn't be better at least...