Samsung announced its new UFS 2.0 memory in capacities up to 128GB just days before the Galaxy S6 was official, so we all correctly surmised Samsung's new flagship would make use of the new, faster storage. Some early benchmarks of devices at MWC show just how speedy the Galaxy S6's storage can be. It just destroys every currently available phone. Maybe you won't even mind the lack of a microSD card when the internal storage is this fast.
The new UFS 2.0 NAND standard offers considerably faster performance than the eMMC that has been used until now. It can read and write at the same time and has command queuing to prioritize tasks. According to Samsung, the UFS chips it is making are capable of theoretical max sequential read/write speeds of 350 and 150 MB/s. That's 1.4 and 1.6 times faster than eMMC, respectively. The numbers presented by Phone Arena certainly point to monster performance from the Galaxy S6.
Using the Androbench app, the Galaxy S6 crushed the Note 4, Xperia Z3, Nexus 6, Galaxy S5, and a number of other phones. Unfortunately, there are no numbers from the HTC One M9 included in the data, but it's still using eMMC, so I don't imagine it will be much different.
Random read/writes don't have much impact on flash memory systems, but the sequential numbers might tell you how a device will perform when working with large files—things like HD video or heavy games. There is, of course, the usual disclaimer that these numbers were obtained from a non-final device on the show floor. Anything could happen between now and release.