I've just upgraded from a 7D, and to go from a burst of 25 Raw to 7 is a little sad! Luckily I've still got my 7D for sports/cropped uses.
I can't see much/any difference of the sustained write speed after trying different cards... The fastest I have is a x600, which seems as fast as a really old x50 card.
x600 should be able to manage 90MB/s and as it's clearly not writing at that does anyone think it's worth trying a faster card? Like a x1000?
If I put in a SD card and set it to automatically switch recording between the two then the buffer jumps to 10, but I've only got slow EYE-FI SD cards... so not sure if thats now another bottleneck!
So yes, throw in an SD card if you want to increase the buffer size... if anyone has a fast SD card can you let me know if it's faster after the buffer?