Rob Gailbraith CF/SD performance database 5D MKIII results
http://www.robgalbraith.com/bins/camera_wb_multi_page.asp?cid=6007-12452
SD Cards
Fastest SD cards were dead slow compared to their rated speed. Write speed in 5D MKIII terrible, but fast cards should still work well in fast card reader during offload. Sandisk Extreme Pro 95MB/Sec cards use SD 3.01 (UHS-1) standard which Canon stated is not supported by 5D MKIII.
Write speed in JPG and Raw, and number of RAW+JPG frames until buffer full.
SD Card JPG RAW Burst
PhotoFast Class 6 SLC - 4GB 18.5MB/s 19.9MB/s 22
Sandisk Extreme Proj 95/MB/Sec - 8GB 18MB/s 19.4MB/s 22
Sandisk Extreme Proj 95/MB/Sec - 16GB 17.9MB/s 19.3MB/s 22
Sandisk Extreme Proj 95/MB/Sec - 64GB 17.9MB/s 19.3MB/s 22
CompactFlash Cards
Lexar UDMA-7 CF cards were blazing fast with Sandisk UDMA-6 cards in second place. Write speed in 5D MKIII very good, with card reader performance even better.
Write speed in JPG and Raw, and number of RAW+JPG frames until buffer full.
CompactFlash Card JPG RAW Burst
Lexar Professional 1000X 32GB 46.8MB/s 80.2MB/s 75
Lexar Professional 1000X 128GB 46.5MB/s 78.7MB/s 74
Lexar Professional 1000X 64GB 46.3MB/s 76.9MB/s 73
Lexar Professional 1000X 16GB 46MB/s 70.1MB/s 67
SanDisk Extreme Pro 128GB 45.7MB/s 68.9MB/s 64
SanDisk Extreme Pro 32GB 45MB/s 60.6MB/s 57
SanDisk Extreme Pro 16GB 44.9MB/s 58.6MB/s 56
SanDisk Extreme Pro 64GB 44.8MB/s 58.6MB/s 55
SD Card to Computer via Card Reader - All Devices
http://www.robgalbraith.com/bins/reader_report_all.asp?cid=6007-9438&card_type=SD
CompactFlash Card to Computer via Card Reader - All Devices
http://www.robgalbraith.com/bins/reader_report_all.asp?cid=6007-9392&card_type=CompactFlash
5D MKIII CompactFlash write speed is very good. SD write speed seems best suited for JPG only or overflow. Hope SD write speeds can be improved via firmware.