Bigger nand chips, bigger buffers, faster times until the buffer fills up.  True.  But.  Measured speed is not the same as user experience, we simply don’t experience time on that short scale.  The only activities where you might be able to clock the difference is in the transfer of lots of large video files (how often do you do that? Won’t make a difference in streaming btw), manipulating large number of photos simultaneously, or compiling a lot of code.  If you do that all the time it may be a consideration.  But even though i do all of the above, it’s rarely, and so to me it’s much more critical I get the right storage size to support my activities…storage capacity impacts me all the time.  256 is not enough for my photography, 512 is a struggle, if I can afford the Apple tax, 1tb is my sweet spot.  YMMV.