[aviator]

The larger 777 can lift much more cargo and carry more passengers than the 767 and fly them to a farther destination. Much better for deployments when it counts. The avionics are close enough not to be a big factor.

[Doe Eyes]

If the Air Force had wanted to carry more cargo and passengers, they would have included those requirements in the Procurement Specification and Boeing would have offered the 777.

Evidently, that was not what the Air Force desired.

The entire passenger area of the 767 is available for cargo/passengers. All of the fuel in the tanker is stored in the area formerly used for baggage/cargo.