Psion said:
Take a look at the high end. Creature CRs are as high as 13.
I generally bounce my results against the existing list and tweak it from there, but I usually get within one of where a creature is supposed to be.
Psion, as I said, this doesn't work until you get to the high end. Once you're up around SMVII and higher, you'll almost never summon a creature with a CR higher than the spell's level.
Olive, a fiendish wolf is the same CR as a regular wolf; a fiendish dire ape is one CR higher, you're right. (I'm used to running a druid, so I'm more familiar with the less powerful SNA spells).
Again, though, I don't think a formula based on CR is the right way to approach this. THere's too much room for munchkinizing the list.
Furthermore, consider as a DM whether you want to make SM completely more powerful than SNA. As it's written, summon nature's ally generally summons less powerful (untemplated) creatures, but the caster has a much broader range of creatures to summon. A cleric casting a summoning spell, OTOH, is limited to the few creatures whose alignment comes close to matching her alignment.
Sorcerers and wizards don't have that restriction -- but then, their spells are *supposed* to be better in combat.
I think my suggestion would be to let a cleric choose three or four creatures of each level that they can summon. They don't need to be the ones in the book, but they need to be very close in power level to the ones in the book. And they can't summon any others.
IMC, for example, the players have been fighting evil clerics of a god whose symbols include scorpions and lizards; guess what critters I've added to these clerics' summoning lists?
Daniel