Using our , we measured transfer speeds from the SanDisk Ultra microSDXC 128GB with IOMeter. Its sequential activity was measured at 44.66MB/s and 14.29MB/s for read and write, respectively, and random large-block performance was found to be 43.98MB/s and 2.45MB/s for read and write, respectively. Both read values were higher than those reported by SanDisk; the company doesn't disclose expected write speeds other than to say they'll be slower than the read performance.
The SanDisk Ultra microSDXC 128GB is perfect for users that desire huge storage capabilities and don't mind lower performance compared to other of SanDisk's microSD cards. The card to which we compared the Ultra microSDXC, the Extreme PLUS microSDXC, provides some perspective for the Ultra microSDXC. With the 128GB Ultra, the user effectively gives up about half of the performance speed for twice the capacity. Potential buyers should be not judge the Ultra microSDXC too harshly on performance though, the card will still accomplish all it is asked in the target use cases.