Does CF card speed affect ALL-I quality on 5D Mark III?

[Policar]

I've read that card speed has no material difference on video quality--it will either record or not record--but I'm not convinced. My years-old, very slow 1GC CF card records ALL-I just fine, but the bitrate seems suspiciously low.

Should I splurge on that expensive CF card or keep recording to my class 10 SD card? I will be recording in ALL-I exclusively. Thanks!

 

[motorazr]

Shouldn't make a difference.

A file is a file. Worst thing is you'll bump up against the buffer much quicker since it'll be taking pictures faster than it can record ... and even in that case it'll just stop shooting until it can take another one.

 

[Policar]

Thanks. I've read that Canon's buffer on the SD card is different from on the CF card (the manual indicates as much) and that maybe you can get 10Mb/sec more on a fast CF card vs a fast SD card? Even if that's the case it seems trivial. For photos I'm sure it matters if your buffer runs out...

My dirt cheap 16GB class 10 transcend SD card has no trouble reaching 90Mb/sec on ALL-I, but I've never seen it exceed it, and I've heard stories of it happening with CF cards.