[abij]

Originally Posted by ZodWallop

I understand that. As I mentioned, I'm not so concerned about boosting the speed. I just didn't want to get a card that would be slower than what's in the Clara already.

I'm looking at these two. Not sure what the difference is, though I'll likely buy the second, slightly more expensive one:

Samsung 64GB MicroSDXC EVO Plus Memory Card w/ Adapter (MB-MC64GA)

Samsung Evo Plus 64GB MicroSD XC Class 10 UHS-1 Mobile Memory Card for Samsung Galaxy S7 & S7 Edge with USB 2.0 MemoryMarket Dual Slot MicroSD & SD Memory Card Reader

I just noticed the two ereaders you mentioned have the same CPU as my Aura HD. The processor is i.MX507 whose documentation says (p. 13)

Up to 200 Mbps data transfer for SD/SDIO cards using four parallel data lines

So any transfer speed higher than the theoretical upper bound 25MB/s will most likely be capped at that point.