This is so awesome to play with!
I have a Mark II, and a Transcend 400x 32GB card. When I run the benchmarks, my write speed is around 37.5-50MB/s, only at 16384k buffer is it under 40, and with the rest it's usually closer to 50. Read speeds are around 65MB/s consistently.
The anomaly is at 128k buffer it's only 25.5MB/s write speed

I'm trying to record at 1280x720 at 24fps, and it says i only need 36.9MB/s to record, however, I only get a few seconds before it starts skipping bad and automatically stops.
Even at 1280 x 540, which says it only requires 27.6MB/s it starts skipping within 10 seconds.
I can record without skipping at 960 x 540, but I still get a lot of magenta blocking.
I tried with both the May 14, and May 16 nightly builds and the 5D Mark II record module and autoexec.bin that someone else posted.
Is there something I'm missing, or is this normal?