I've tried using a M3 firmware on R4 without success, it turns on, but a message pops up say 'Hardware not Compatible' I've read in the forums, that a hacked one will work, but as for now the 'clean' firmware doesnt work, its what i expected anyway, but many others wanted to know I have downloaded both firmwares M3 & R4, and by looking at them, all the files apart from 1, the (_DS_MENU.DAT) have exactly the same files (no. of files, names, size, modified date & time are identical), the _DS_MENU.DAT i assume being the actual firmware isidentical aswel in size aswel the only differences from both is the modified date & time.are not the same. This info might seem irrelevent, but from looking at hardware, firmware and accessories, the M3 & R4 are really the same. Someone on scdev.org made that point about the names of the cards, M3, G6, R4, all cards with a single letter followed by a single digit!!