I recently bought a Canon 5D Mark III body on the cheap for $2699 from a Canon authorized dealer during the 2013 holidays. I also got camera goodies to go with it. Free shipping. It was too good to pass up. I had a Canon 50D for about 5 years and it was having mechanical problems, so it was time to move up.
There was one issue that I read about and it was about the write speed for the SD card. The write speed for compact flash was good, but SD card write speed was subpar. So out of curiosity, I did some write speed measurements from my 40D, 50D, and 5D Mark III and see how they looked. I had a handful of memory cards, not many, so this is not an extensive test.
Testing
To setup, I set to manual mode, set the shutter speed to 1/8000 sec, and set the drive mode to high speed. I set the image format to RAW. (I photograph RAW all the time.) I format the flash memory for each card. I left the camera lens cover on, so there is no lens attached to the camera.
To test, I held the shutter button down for 30 seconds. After 30 seconds, I monitor the red light on the camera. Once the light is off, I log the time.
Canon 40D
| Compact Flash | # of shutters | Time (sec) | Total Bytes | Write Speed (MB/sec) |
| Lexar Professional 64GB 1066x | 49 | 38 | 431,526,421 | 10.8 |
| Lexar Professional 64GB 1000x | 49 | 38 | 431,544,418 | 10.8 |
| Duracell Pro Photo 32GB 600x | 47 | 40 | 422,914,089 | 10.1 |
| Lexar Professional 8GB 300x | 46 | 40 | 413,916,208 | 9.9 |
| RiData Lightning Series 32GB 233x | 40 | 42 | 359,952,888 | 8.2 |
| RiData Lightning 16GB 233x | 41 | 43 | 368,910,272 | 8.2 |
| Kingston Ultimate 16GB 266x | 46 | 40 | 413,910,593 | 9.9 |
Canon 50D
| Compact Flash | # of Shutters | Time (sec) | Total Bytes | Write Speed (MB/sec) |
| Lexar Professional 64GB 1066x | 105 | 34 | 1,699,319,781 | 47.7 |
| Lexar Professional 64GB 1000x | 111 | 34 | 1,723,978,375 | 48.4 |
| Duracell Pro Photo 32GB 600x | 53 | 44 | 837,474,530 | 18.2 |
| Lexar Professional 8GB 300x | 69 | 38 | 1,090,239,240 | 27.4 |
| RiData Lightning Series 32GB 233x | 50 | 43 | 789,865,187 | 17.5 |
| RiData Lightning Series 16GB 233x | 53 | 44 | 837,224,823 | 18.1 |
| Kingston Ultimate 16GB 266x | 47 | 45 | 742,417,602 | 15.7 |
Canon 5D Mark III
| Flash Memory | Type | # of Shutters | Time (sec) | Total Bytes | Write Speed (MB/sec) |
| Lexar Professional 64GB 1066x | CF | 138 | 33 | 3,147,136,648 | 95.3 |
| Lexar Professional 64GB 1000x | CF | 138 | 33 | 3,146,455,481 | 95.3 |
| Sandisk Extreme Pro 64GB | CF | 138 | 33 | 3,146,779,170 | 95.3 |
| Duracell Pro Photo 32GB 600x | CF | 48 | 42 | 1,113,530,223 | 25.3 |
| Lexar Professional 8GB 300x | CF | 64 | 38 | 1,484,841,046 | 37.3 |
| RiData Lightning Series 32GB 233x | CF | 43 | 43 | 997,486,322 | 22.1 |
| RiData Lightning Series 16GB 233x | CF | 44 | 44 | 1,020,629,518 | 22.1 |
| Kingston Ultimate 16GB 266x | CF | 37 | 48 | 858,341,337 | 17.1 |
| Kingston 32GB | SD | 27 | 61 | 615,675,325 | 9.6 |
| Patriot Signature 64GB MicroSD OEM | Micro SD | 27 | 58 | 615,666,701 | 10.1 |
| PNY 64GB microSDXC Class10 UHS-1 | Micro SD | 34 | 49 | 774,943,851 | 15.1 |
| Sandisk Extreme Pro SDXC UHS-I 64GB | SD | 41 | 45 | 934,784,686 | 20.8 |
Flash Card Reader
I decided to measure the read/write speeds by using a Transcend USB 3.0 card reader. I used the ATTO Disk Benchmark with the Direct I/O setting, the Neither setting, and a transfer size of 8192KB. The following are the results:
| Flash Card | Type | Write Speed (MB/sec) | Read Speed (MB/sec) |
| Lexar Professional 64GB 1066x | CF | 126.9 | 145.9 |
| Lexar Professional 64GB 1000x | CF | 126.3 | 148.9 |
| Duracell Pro Photo 32GB 600x | CF | 38.5 | 89.5 |
| Lexar Professional 8GB 300x | CF | 47.3 | 43.3 |
| RiData Lightning Series 32GB 233x | CF | 23.6 | 45.4 |
| RiData Lightning Series 16GB 233x | CF | 24.0 | 45.3 |
| Kingston Ultimate 16GB 266x | CF | 38.4 | 48.4 |
| Kingston 32GB | SD | 10.4 | 23.1 |
| Patriot Signature 64GB MicroSD OEM | micro SD | 15.3 | 46.9 |
| PNY 64GB microSDXC Class10 UHS-1 | micro SD | 21.6 | 87.4 |
| Sandisk Extreme Pro SDXC UHS-I 64GB | SD | 90.8 | 96.9 |