Referring to the original question, I think it's not obvious that the OP refers to inverting buck-boost as introduced in post #13. It's not clear if the inverting topology is appropriate.
The initial post asks for efficiency. I conclude that synchronous topology (transistor switch instead of diode) should be preferred. Also routing the total transferred power through a storage inductor as in inverted buck-boost or flyback should be avoided because it involves additional losses (higher copper and core losses, increased switching losses due to higher peak current and switch voltage).
Respectively, if you need buck-boost operation, a four switch converter is the most efficient solution.