I'm missing something here. The maximum power transfer theorem states that max power transfer from source to load happens when source impedance matches load impedance.
In the case of a 10V source with an impedance of 5 ohms driving a load impedance of 5 ohms, power transfer to the load would be 5 watts, for an efficiency of 50%.
In the case of a 10V source with an impedance of 1 ohm driving a load impedance of 9 ohms, power transfer to the load would be 9 watts, with an efficiency of 90%.
This seems to contradict the theorem, what am I missing?