I put in an order for some new CF cards the other day, and while running them through their quality test I noticed something interesting. While otherwise rated the same, performance between the 32GB and 64GB 400x Transcend CF cards is not identical.
This isn’t so strange really. It’s pretty common for larger capacity flash memory devices to outperform lower capacity units in the same product line. (This is especially true among SSDs, where 128GB and 256GB models perform much better than 32GB and 64GB models.) The performance difference did not fit the usual pattern though, so I investigated further.
The short version of this article is this:
The 32GB cards are faster at READING data, but the 64GB cards are faster at WRITING data. All cards perform reasonably well, so if capacity is your primary concern get the 64GB cards. If downloading images to your computer quickly is your primary concern, get the 32GB cards. If performance while burst-shooting (flushing data quickly out of the camera buffer) is your primary concern, get the 64GB cards.
Here’s a chart with the details (click for a full-res version):
As you can see, the 32GB cards average 117.5MB/s for downloading to your computer, but with an average write speed of 49.05MB/s, they’ll flush the camera buffer more slowly than their cousins. The 64GB cards have a slower average read speed of 98.38MB/s, but they’ll flush your camera’s buffer faster with an average write speed of 67.52MB/s.
Bear in mind that if you’re shooting on the Canon 5D mk III and writing the same data to an SD card, worrying about write performance of your CF card is a waste of energy.
Testing Methodology (the nerdy stuff):
I had three copies of the 32GB 400x Transcend CF cards, and three copies of the 64GB 400x Transcend CF cards. I formatted all the cards in my Canon 5d mk III, then tested them on a full USB3 chain using CrystalDiskMark. Each card was tested five times with a 1,000MB data set. The charts represent the average of five tests on each card. The reader was a Transcend TS-RDF8K USB3 card reader. The benchmark computer was a hexa-core i7-3930K @ 3.2GHz, 32GB RAM, Asus Rampage IV Gene w/ integrated USB3 running Win 8 Pro x64.
I don’t have as many copies of other brads/models of memory cards, but I’ll put up benchmarks from some other options when I get a moment.