I couldn't find anything when I searched, so sorry if this has been asked before.
I am trying to figure out the best way to go in buying CF cards for my Mark3. I was looking at the Kingston 266x cards and comparing them to the Lexars with the huge rebates now at B&H.
I don't think it matters much. I wandered into BB and just grabbed an 8gb card of each type, shoved them into the camera and they work fine. Without looking I couldn't tell you what kind they are.
You may shave 2-3 frames in a burst on the write but where faster cards pay off is the transfer to you PC. I used a 133x on a usb and it took about 15 minutes to transfer 8GB, a 300x with firewire takes less than 3 minutes.
I have been using transcend cards for 3 years with no issues.
Sandisks are over rated, lexars are way over rated.
The 1D III isn't UDMA enabled (good one Canon) so other than speed in downloading from a reader, the non UDMA cards are just as good in camera and cheaper.