The normal HDD-drivers default to UDMA-4, and that is also used when the mode isn't changed. Also there propably wouldn't be any speed increase using UDMA-5 or better modes.
For the DMA-selector I just have no idea why it doesn't work for some PAL-users.
I tested it with PCSX2 using BIOS-files from various versions of consoles and with/without NTSC-patch. I have a non NTSC-patched version of HDL in my PAL V5 and it's launched from the memorycard with the old DMS MC Explorer and the selector also works there just fine.
--- Signatures are just lame excuse to waste bandwidth ---