1Dx: what's the "right" CF card?

[neuroanatomist]

I also have Sandisk Extreme Pro 16gb cards which are UDMA 7 90MB/s.

I use a set of three Sandisk Extreme Pro 32 GB 90 MB/s cards. I write RAW simultaneously to both cards, the card on slot 1 gets swapped with the third card, the card in slot 2 stays in the camera as a backup until the files from the other card are on the computer and backed up to two external drive. That way, I never have fewer copies of every image.