M3 Media Card Compatibility at the M3 Wiki
http://m3wiki.emuparadise.org/index.php/Media_Card
Covers the M3 CF, SD, and miniSD with DMA, firmware revision, whether or not GBA mode works, and how well the Castlevania: Dawn of Sorrow opening video performs.
It does not cover FAT12/16 vs. FAT32...