Using a 90mb extreme pro Sandisk CF card, and shooting raw, with a minimum of 1/500 shutter, wide open, fully charged battery, and good exposure to reach the maximum continuous shooting speed of 6fps, I manage to get between 18 - 23 shots. This is about 3 to 3.8 seconds of shooting and it was achieved even with ISO 800 (which increases the file size). It takes about 4-5 seconds to clear the buffer when full (didn't time it with a watch, just mental estimate
When I was reading about the 1DIV tests with the same card, looks it manage to get about 25 - 30 shots which translates to 2.5 to 3 seconds. From the specs, it seems that even the 1DX won' t manage to do better than that due to it's fast 12fps.
It was interesting to read the digital picture reviewer saying that he used to prefer shooting sports with the 1DsIII with it's slow 5fps instead the 1DIV, so that he get more background blur due to the sensor size difference. This was one of the main reasons I wanted to switch to FF for sports. Now, the 5DIII can give a 6fps with the best AF and and great FF sensor. It is also interesting to hear that the new 5DIII AF has better odds to get the photos in focus compared to the 1DIV.
I want to add that I am noticing that when the 5DIII battery is below 40-50%, the continuous shooting speed sounds to be about 4fps. It made me think about the battery grip rumor saying that the camera could achieve 6.9 fps with it. Anyone noticed the same fps decline ?