You need a card that makes use of the 64bit PCI slot for best performance.In my G4 I use a flashed cheap Sil3512 card(flashed using my Mac btw). I can boot OS X off it too.
My card is only 33MHz 32bit; though it is faster than the onboard PATA of my Digital Audio. A MDD has faster PATA and could probably beat my card but I would not actually be upset about using it over the onboard PATA due to the other significant advantages.
but then, you know, I am a sucker for being able to use cheap new hardware in old systems as well as nice thin single platter drives in applications where I do not need a super crazy fast drive.
