My 5D MkII take only CF card also, and I have 5 CF cards at 4 different speeds (133X~1000x). They all take video equally well and the different between them is slight in burst and write speed that doesn't affect my shooting style at all. IMHO, the only people that may need the fast expensive cards are sport photographer that constantly shoot in bust mode, and have the 1D MkIV (10 fps), or 7D (8 fps). 5D MkII only get 4 fps.