These cards aren't backwards compatible with CF cards or cameras that use them. These are part of a standard that was announced back in 2008 as a successor to CF. They use the faster SATA architecture as opposed to the PATA architecture of CF and have SATA connectors.
The 256 GB ExtremePro card that was just announced is the conventional CF type not CFast so those read/write times are not reflective of the new CFast cards.
So unfortunately, while it is good to dream that you will get great raw video framerates with such cards. The hardware is not compatible with the 5d3.
stratocaster0811 got a reaction from Julian in New 3000x Sandisk Compact Flash cards to supercharge raw video on 5D Mark III