Someone asked about some testing - well - here is what I've found from testing on both the 5D3 and the 1D4:
5D3 - RAW - UDMA 7 - "rollover" to SD after CF is full:
26 frames till full with the buffer emtying in just over 3 seconds
1D4 - RAW - Firmware 1.1.1 - UDMA 7 - rollover to SD after CF is full:
31 frames till full with the buffer emptying in just over 6 seconds
I just verified that it makes no difference if I pull the SD card - the writing to the CF is the same.
I really wish the guy who wrote the original blog post that started this had clarified his title - I think it should have been:
"Why you should not
put write to
an SD card in your Canon 5D Mark III (if youcare about speed)"
If you want my testing gory details - here is my blog post about it:http://blog.willshootphotography.com/2012/06/udma-7-cf-card-performance-on-canon-5d-mark-iii-and-1d-mark-iv-soooo-worth-it.html
I'll be candid and say I don't have a problem with the SD not supporting the superfast SD protocol - primarily because I'll always just use it as a rollover, not as a primary "write to" card type. I know that CF is faster than SD and that is what works for me. I'm really glad that Canon put dual SD in 1DX - it never made much sense to me to *not* have two of the same card reader in the camera other than for space restrictions... and it doesn't take up *that* much space...