AFAIK, MCGA has nothing to do with Mode-X. Mode-X was 320x240, and was achieved by manipulating VGA settings. MCGA supported Mode 13h, but I see no evidence that it could be manipulated to output 320x240 or that it supported planar memory, which is generally considered synonymous with Mode-X. In fact, from what I can tell, MCGA didn't have enough memory to support planar mode.