Card speed in the 1D Mark IV

Recently my camera buffer filled up when I was shooting picture of Willet in flight. Needless to say that sort of thing really didn't happen very often with the sluggish 5D Mark II, but the 1D Mark IV is a different beast. Since Rob Galbraith appears to have slowed down or stopped updating his CF card database I'd become curious which were my faster and slower cards in my new 1D Mark IV and got a surprise. I did a test where I shot the camera until the buffer filled, and counted how long it took to empty the buffer (the red write light goes out). All cards were Sandisk.

CF Extreme 60 Mb/s 16 Gb - 9 secs - this card bought in 2010
CF Extreme IV 4 Gb - 12 secs
CF Extreme III 8 Gb - 16 secs
SD Extreme III 8 Gb - 24 secs
CF Extreme III 4 Gb - 24 secs

My cards are an "evolved" mix of different ages, so the older CF III 4Gb is several years old, the other cards one to three years old. Even with the same labeling the Sandisk cards have different speeds depending on their age. With the 1D Mark III the SD cards were comparable with the CF cards because the CF slot lacked UDMA compatibility, which was only introduced with the 1Ds Mark III. However the 1D4 has UDMA so the CF cards have become relatively a lot faster. At some point you do hit the speed limit in the camera card slot itself, of course.

The speed ratings from Sandisk's own truly unfriendly website show this story too:
CF Extreme Pro are 90 Mb/sec
CF Extreme are 60 Mb/sec
CF Extreme III and Ultra are 30 Mb/sec
SDHC Extremes are 30 Mb/sec in some versions
SDHC Ultra are 15 Mb/sec

These are current models, some of which seem to come in various grades, but the upshot is that Sandisk's very fastest CF cards are three times faster (!) than their fastest SD cards. The B+H site appears to be one of the better ones for surveying various CF and SD card rated speeds and their price points.

Slashgear tested CF cards in the 1D4 and show that you can get a 1D4 to write at 57 Mb/sec onto a card rated at 90 Mb/sec. That's slightly more than 3 images a second. It seems there's no point in buying an Extreme Pro card for speed - I'm getting roughly that speed with my regular Extreme - we've reached the inherent speed of the 1D4 card slot. Slashgear either didn't realize that or only had the fast cards to test. In their companion piece on SD cards, they get about 20 Mb/sec over all cards, which is around 1.2 images a second. Since the 1D4 usually fills the buffer with 33-34 images, the 24 seconds it takes my existing SD card to clear is pretty much par for the course. No room for improvement there.