As Caledonian mentioned, you want a balance of optional characteristics. This is determined both by heat treat and alloy composition. When heat treating, you must balance hardness and toughness. The better your treatment is, the higher each value will be, (the opposite is true for a poor heat treat), but it is ultimately a tradeoff. There are other factors to consider as well. I learned that there are two different tempering methods to bring CPM154 to 60-61; one produces a much cleaner blade than the other, requiring less finishing time.

There are also characteristics determined more by the alloy. These include abrasion resistance and corrosion resistance. This is why, even in an annealed state, 440a won't rust and A11 will trash your grinding belts.