summon monster

[Li Shenron]

The key to Summon Monster should be ECL, not CR or HD.

I am not sure. Summon Monster spells last too short, and therefore they are almost always used in combat. ECL doesn't play that much part in this.

Occasionally (in my own experience, quite rarely) you may want to summon a monster with a specific ability to let you overcome a single challenge. For example, you may want to summon a creature who had Knock at will - if such creature exists - if you really need the spell but you don't have it, or a creature immune to fire to retrieve an object which is inside a river of lava. This kind of abilities can belong to creature of any CR or ECL however, and you may find yourself in need to use any spell between SM I and SM IX, therefore this could not either be the basis for those lists.