Canon have just released this update which when applied to the camera will improve performance with UDMA 7 type cards. There are other bug fixes too so its worth doing.
You can download the new firmware from here:
(select the firmware button then click on either the OSX or Windows link that shows up)
Be sure to follow the advice given to the letter to install this, if in doubt add it to the list of items to do when I’m next onsite with you.
Stephen