I've recently tested one 5D3 in the same store I bought my body. As I thought, the problem showed up in the same moment as in my camera, so 49%. FPS slowed from 6 to 3 when reached the level. I checked the SN and, I was suprised by the way, there was only one number differing from my SN, in the end, so it was the next body produced after mine. So, because of that I want to test another bodies in the future.