MicroSD Performance in Canon 5D Mark II
I searched high and low for really definitive performance specs on how well SD (both normal and MicroSD) cards perform in a DSLR using a converter. I know many people out there will go, "Why on earth would you want to do that? You'll lose performance etc...". The short answer is,
1) It's a lot easier to find a portable backup device for SD cards than it is compact flash that you can interface with your iPhone/iPad
2) I wanted cards that I could interchangeably use between my GoPro Hero 3+ and my Canon 5D Mark II.
3) Most of my photography is landscape photography/nature/timelapse. If I'm really looking to do some fast action stuff, I'll pop in a fast CF card, but 95% of the time, speed isn't a consideration.
So, I purchased this: http://www.bhphotovideo.com/c/product/816112-REG/EXTREME_SD-HC-XC_TO_CF_ADAPTER
It converts SD/HC/XC to compact flash (obviously I had to use a MicroSD to normal size converter as well. The first thing I noticed was that this was a thicker compact flash card than normal - about as thick as the little microdrive compact flash cards were that came out some time ago. These will be too thick for many card readers/devices, but most cameras (including the Canon 5D Mark II) can accommodate.
For this test, I used 2 different types of MicroSDXC cards, one was a Lexar 600X 64gb MicroSDXC card. The other was a Samsung Pro 64gb MicroSDXC card. To start off, there was not a discernible difference in speed between them really. You may have different luck/results with other cards but here were my findings:
1) Write speeds were about equivalent to a 133X Compact Flash card. When shooting large RAW+JPG photos, once the buffer filled up, it took about 2-3 seconds to write each photo to the card before I could take another.
2) Recording 1080P video was no problem. At no time during testing did the buffer show or fill up even after introducing fast motion to try and bump up the data rate a bit.
3) Read speeds were considerably better and were close to 266X when copying the files off the card.
Overall, performance was acceptable. If speed isn't a huge consideration, this may be an acceptable path for you to pursue if you wish to consolidate the types and numbers of cards you are using for your various devices.