I am finding there still is some confusion as to camera speeds and memory card speeds.
So first, let's look at digital camera speeds. All cameras that shoot RAW and JPEG will shoot both formats in all drive speeds, but because of the file size differences - whether you shoot RAW, JPEG or both at the same time - will affect how the camera handles multiple shots. As the camera shoots at high or low drive speeds, the camera will often shoot faster than the files can be put onto the memory card. The files are then put into a buffer (memory in the camera just for this purpose) to wait in line to get on the memory card. When that buffer is filled, the camera will stop shooting until room is made for the shots.
With RAW, the buffer fills quickly because the image files are large, which means that after a certain number of shots, the buffer will be filled and there is no more room for additional image files, so the camera will quit shooting. With JPEG, the buffer fills more slowly because the files are much smaller, and often the memory card can keep up with the JPEG files so the camera does not quit shooting. This is a big reason for the L or low speed setting on many cameras — since shots are taken slower, the buffer fills more slowly, even with RAW, so you can keep shooting longer than with H or high speed.
Memory card speed affects how fast the camera can pull images out of the buffer and load them onto the card. A faster card will allow the buffer to be emptied faster as long as, and this is an important qualification, the camera has been designed to handle the speed of the card. If a card is faster than the capabilities of the camera, that speed is wasted as the camera cannot go that fast. Using a high-speed memory card with a camera that cannot work that fast will have no effect on camera speed and will give no better results than a lower speed memory card.
Most mid-level to high-end cameras typically could handle the speeds of cards available at the time the camera first came to the market. But then this capability will change over time as card speeds increase during the life of the camera model.
Memory card speed has no effect on how fast the camera can shoot — that is purely a function of the mechanics and electronics of the camera. It can only affect how fast the buffer is cleared, which will affect how long the camera can shoot before it has to stop and allow the buffer to open up.
Note: Rob Sheppard is an instructor at BetterPhoto.com, and teaches many excellent online photo workhops, including Guaranteed Better Photography, The Magic of F-stops: Choosing the Right Aperture, and Storytelling Nature Photos. In addition, BetterPhoto's photography school offers online DSLR camera courses on specific Nikon, Canon and Olympus digital SLR cameras.