With all due respect . . .
1. SoL is not SoD. The only time there's little difference between the two is when you face a single opponent and have the convenience of disposing of them.
2. Painful Slumber of Ages ends the moment the target takes damage; Word of Changing allows an additional save (and the target might run away).
3. Both invocations have no effect on a successful save.
4. About 50% of the opponents you'll be facing at those levels (undead / constructs / planar / plants) ignore both invocations.