A few of us tested this awhile ago. The short answer was that the camera itself becomes the limiting factor after a certain point (~50 MB/sec for the 7D and ~60 MB/sec for the 1DIV). So faster cards will not help in camera, but should help when transfering to your computer if using a good CF card reader/etc.

Here is a link:
http://community.the-digital-picture...?t=5294&page=8