The easiest way to explain my question is through a metaphor. This is a little weird but bear with me. When you play COD or some other shooter the guns each do different damage in the same way that different coolers have different levels of efficacy. 25 dmg is an important cut of point along with 33 and 50. If a gun does 24 dmg it will take 5 bullets to kill and if a gun does 25 dmg it will only take 4. Therefore this 1dmg difference makes a massive difference in the efficacy of these guns. Conversely a gun that does 32 dmg is really that much more effective than one which does 26.
So on to my question. I was recently reading a of a review of the swiftech watercooling kit (which performs better than an AIO) compared to the top air coolers. All of the coolers where basically much of a muchness. Water did better a bit better than air temp wise but was a bit noiser. So for arguments sake let's say that most of the best coolers are within 5 degrees of one another (a reasonable assumption). Could 1 degree on an overclock be the difference between stability and instability or is stability more on a sliding scale.