Yay! Another thread to hijack with boring P/S bookkeeping bureaucracy!
Under what's commonly called “butters”, cocoa butter is special, since it is the only one that brings appreciable amounts of palmitic acid. All others are high-stearic, but (relatively) low-palmitic. That's why I choose cocoa when I don't have another source of palmitic acid (like rice bran/cotton/palm oil, or Japan wax) in my recipe. If I do have one of the aforementioned in some quantity, cocoa butter would be kind of redundant, and shea/sal/kokum/mango/cupuaçu butter or soy wax (hydrogenated soy/canola/sunflower) work quite as well.
That's all based on pure palmitic/stearic bureaucracy. I don't like imbalanced P/S: too P-heavy gives soaps that tend to not harden up, and dissolve quickly in water, too S-heavy makes my skin feel chalky and dry. There really isn't a way around this except trying out for yourself. BUT if your recipe is high in lard/tallow (both with balanced P/S), you can safely forget about all this.
Another thing to keep in mind with shea is
unsaponifiables. Only a few oils contain appreciable amounts of them (olive, avocado, shea, rice bran), and if a recipe makes use of them as a “secret superfat”, they're difficult to replace.
But with your situation in mind, I have good news for you: a good way to smuggle something similar to unsaponifiables into a soap is: beeswax!
tl;dr: P/S ratio doesn't help you decide in favour of cocoa butter, and unsaponifiables don't help you decide in favour of shea. You're free, do whatever you want!