The website http://www.cameramemoryspeed.com/ may provide the answer and can also provide a plethora of interesting and worthwhile information regarding memory cards and their relationship with many digital cameras.
Here is the website introduction:
"We test SD cards and CF cards in cameras to evaluate performance. Fast cards allow your camera to take more pictures in less time as well as transfer images to your computer faster. Buying a fast card does not guarantee high speed, your camera may be a limiting factor. We test a variety of memory cards in each camera to find the best cards. We also test several card readers with different memory cards to find which readers work best for each memory card."
Unfortunately, my Canon 6D2 is not one of the cameras that has been reviewed. However, I did learn that the two fastest CF cards for my 7D2 (as per the 2014 test date) were the Lexar Professional 1066x 32GB and the SanDisk Extreme Pro 160MB/s 32GB.
The site provides information such as: "The 7D Mark II maintains a high frame rate longer when using faster cards. In continuous shooting with a fast CF card, the camera captured 28 30MB RAW files at high frame rate before slowing to approximately 3.5 fps for the remainder; while the slowest card reached only 20 shots before the frame rate slowed to a dismal 0.36 frames per second."
What this site does document is that CF cards are generally available in faster speeds than SD cards. I really don't like SD cards (for multiple reasons) and wish that my 6D2 used CF cards (or even better - dual SD and CF cards like my 7D2).
I think that this site might be worthwhile to peruse and to bookmark for further use...