"Effective hashrate" will always go up and down and be inconsistent, because it is affected by luck (i.e. how quickly you solve problems, as opposed to the current around 51 second expectation).  The reported hashrate is the only one you can truly adjust by working with your overclock settings.  Memory clock doesn't help true hashrate that much, but the other clock is pretty much directly tied to the best hashrate you can get.

My 1060 6GB got 18.8MH/sec out of the box, but I have it up to 23MH/sec after playing with the overclocking settings until I was truly weary.  Over 20% of much better than most cards are going to see even with the best overclock adjustment settings, so I am lucky or as some say "won the silicon lottery", since I use a generic HP card.  Fortunately for me, they are built by Samsung and have Samsung memory - it makes a difference, if only a little.  Memory clocks don't make that big a difference, but it does let you make other adjustments you just can't get with Hynix or Micron or Elpida DDR5.  My Asus 1080 has Samsung DDR5X memory, so I expect it to be a great performer, even though I am told that - in general - 1080's don't do as well as others relative to hashrate performance.  We'll see...