Thought i'd do a quick test to show the different write speeds of the Sandisk Extreme and Ultra cards in my 50d. As you can see, the write speed of the Extreme is significantly faster, even though I ended up taking more pictures (28 instead of 26).
As I mention in the video, this is in RAW format and at fixed ISO 100 to ensure the maximum burst is achieved from the camera (no in camera noise reduction).
Cheers!