Testing Results: Sandisk SDHC Class 2: 17.82 seconds IO Data SDHC Class 2: 11.09 seconds Toshiba SDHC Class 4: 15.01 seconds Panasonic SDHC Class 2: 11.40 seconds Transcend SDHC Class 6: 11.25 seconds ATP ProMax SDHC Class 6: 8.50 seconds Testing Method: The data below was derived by timing how long it took the Nikon D80 to write out 6 RAW images using "continuous shooting" mode. Timing commenced when the camera's card status light illuminated, and stopped when the light went out. All cards were formatted in the camera prior to testing.
www.dslrfilmnoob.com This is a quick bit of information explaining what you need to look for in Compact flash card speeds in order to shoot HD video on your Canon 7D camera. I've tested several brands and found that 133x is just fine for video mode on your canon 7d.