I really don't know but I was using 1GB Ultra II cards with the ZD and when upgrading i was considering the Extreme IV option too. You can take a look at Rob Galbraith speed test to make an idea on other cameras. I finally did buy some 4gb extreme III, and I can tell you I don't find any difference between Ultra II and Extreme III so I'm happy I didn't buy the new IV, the price gap is considerable. I've also tried a 4GB Adata card, it worked fine until one day it died. They look so fragile. And they are!!
Regards.
Arnau.