The vast majority of LCDs are VESA's 60Hz VGA standard refresh rate only. Very few NuBus Graphic Cards from the 68k era support 60Hz at all and only 640x480 a/o 800x600 if that. Can't think of a single one from the 1991 time frame at all offhand. If an LCD supports the oddball "flicker-free" Mac refresh rates of 66/75Hz it'll "just work" and if not never will for the most part. I've never run across an LCD that supported multiple resolutions that didn't auto-adjust on its own.

I don't think it was until the Radius/Apple 24AC twins that 1024x768@60Hz was supported by the Mac. Radius and others supported it with earlier cards, but the 24AC was Apple's first offering, IIRC. Still feeling Stuffed, Sleepy and Stupid after Thanksgiving, so don't hold me to it. :

http://home.earthlink.net/~gamba2/vid-mon-matrix.html#party