I recently switched from a PNY Class 10 card to a Sony UHS-1 card (rated for 45 MB/s writes) in my NX100, and a noticed a difference right away. With the PNY card, there was often a long buffer lag after a shot, during which some of the control menus became inaccessible: the display was on, but I couldn't change ISO, WB, etc. After a series of shots, the delay could become quite long and noticeable. But with the UHS-1 card the delay is much shorter, which makes the camera more usable (it's easier to try the same shot again with different settings). I always shoot RAW, which of course means the writes take longer.