I notice that the AT needs a strange speed to be able to properly detect it's the 'correct' speed. The board is set to 6MHz, but requires to be set to exactly 7.2MHz to rougly match the BIOS's required speed(as is documented in it's source code)?

Is this pure coincidence it's matching always at such a round MHz number, or does that mean that the DMA is too fast?

The speed difference is strange: it needs to be exactly 20% faster than what it's supposed to be to match it's checked against speed(from the source code of the BIOS itself)?