Have they ABX tested different brands and memory size of SD cards?
Yes. With DSD recording, whatever the storage medium, it has to support close to 100 MB/sec, but at the very least 90MB/sec in order for the recording to be glitch-free, without hanging, etc, etc - which are all no-no during the actual recording of a master. The advantage of storage without moving parts and susceptibility to vibration in portable recording is an obvious one.
I am still struggling to get time to test if one card ( (Sandisk Extreme Pro 32 MB 95MB/s
http://www.sandisk.com/products/memory-cards/sd/extremepro-sdxc-sdhc-uhs-ii/ ) can do it in order to replace the HDD in Korg MR-1 and MR-1000. I have the required adaptors/cables for years, but back then only the Hoodman card ( IIRC 16 Gb at approx $500) was fast enough. The price was deterrant enough not to try it.
Again, NO in science threads soooo beloved ABX-ing possible - because in this application, card either works - or it doesn't.