Upload & Sell: Off
I read somewhere (I don't remember where) that the minimum write speed you need for the 5D Mark II is about 8Mb/s. So some of the older "Ultra II" type of cards might not be quite up to the task. Use Rob Galbraith's CF testing figures to determine where each brand/type of card fell:
That said, I personally prefer UDMA cards. The camera clears the buffer more quickly with faster cards and does it most quickly with UDMA cards. You don't have to get the very fastest UDMA card, any UDMA type card would be a safe bet. Granted Extreme III type cards are pretty darn quick and perfectly fine for the 5D Mark II. But there is one area where UDMA cards shine even more.... when copying the files to your computer. I use SanDisk's Firewire 800 UDMA CF reader. It is BLAZINGLY fast! It dumps a full card off so quickly it's actually fun to watch! Again, see Rob's testing of the various cars for reading with CF readers, including the Sandisk Firewire 800 model, which generally tested fastest (scroll to the bottom for the test results):
All of that said, yes, UDMA (Extreme IV) cards are quite a bit more expensive and don't offer that significant of a difference IN the camera over, say, an Extreme III card. But they DO clear the buffer more quickly, as Rob's testing shows. But, again, the biggest benefit of UDMA is how blazingly fast they can be read to the computer (with a the appropriate UDMA reader). Even though my 1D Mark II doesn't support UDMA, I bought UDMA cards about a year ago simply for the faster reads. I know after a full day of shooting with 4-5 FULL cards, the last thing I want to wait on is the computer copying the images. I'm tired and I just want to look at my images.