Hello, can anyone tell me if using sandisk extreme pro SD cards will work using a 5D Mark III to record HD raw video?
No. Canon decided to implement a very slow SD-interface configuration and you won't see anything beyond 25 MByte/s.
a1ex managed to unlock this limit and 50 MByte/s seems to be possible. But that feature is not yet supported in available builds and won't give reasonable bandwidth.
Go CF. 1066x, SanDisk, Lexar, Komputerbay.