Originally Posted by
JorgD
A similar question about CF speeds was asked before, and here was my response to the question 7 weeks ago, which I think still applies to the current question.
I use an Extreme III card rated at 30 MB/sec and and Extreme card rated at 60 MB /sec. When I got the Extreme card, I wanted to see how much faster it really is compared to the Extreme III card, so I ran some tests at my PC with my USB card reader. The 30 MB/sec card was faster than the 60 MB/sec card.
This result was of course slightly disappointing, so I started doing more research on this, starting on the Sandisk web page. It appears as they their wording and testing procedures changed over time. The Extreme III card has a through put of at least 30 MB/sec, the Extreme card has a throughput of up to 60 MB/sec. Looks like the words "at least" and "up to" actually cross over for me.
Doing further research, the 60 MB/sec card uses an UDMA interface rather than the PIO interface of the older cards. Now, unless your card reader can make full use of UDMA (which mine obviously could not), you will end up with no better and possibly worse performance than the older cards.
Testing both cards in my 7D shooting Raw images, both cards allowed 22 shots to be taken at high speed before the camera started to slow down. The stated buffer for the 7D is 15 raw. So from the cameras perspective there was no difference at all. Even shooting 1080p movie mode with the 7D, provided your card can accept at least 8 MB/sec, you will have no problem taking movies to your hearts content.
I recently purchased a Nexto Extreme external HD with card reader, and the Nexto could back up the images significantly faster from the 60 MB/sec card than the 30 MB/sec card, causing me to believe that it does make good use of the UDMA interface.
I personally would not spend a lot of money on a faster card as the camera can't make use of the faster speed and the USB 2.0 interface is also slower than most cards so you won't see any benefit there. The only time there is a benefit for higher card speed is if you have a UDMA enabled backup device like a Nexto, or if you have a UDMA CF card reader connected to Firewire 800 or USB 3 when it is released.