Raw video with EOS 550d setting speed writting

[jeanbon2]

Hi
I've checked all the subjects and didn't find any answers.
I use a SDHC class 10 Transcend 8gb and I can record at 15,7 Mb/sec flawlessly with an EOS 550d. At this speed ML shows this speed in green. I bought two SDHC one SanDisk Ultra certified 15 Mb/sec writting 16gb and one PNY high performance certified 20Mb/sec writting, for both cards ML allows only 9 Mb/sec (green writting). I've tried to set a speed of 12Mb/sec it fails after two seconds.
If you have any idea.
Thanks