VW has said,
at least on modern Turbo-EFI engines that are much smaller in displacement,
that a mild boost in the range of 2 to 4 PSI
gives the best fuel economy at highway cruise.

You would need a low numerical gear ratio to get to that boost,
unless you were cruising at a high speed.

With such a low boost
that also means that another 8 to 12 psi is available for climbing hills as 'reserve torque',
whereas with the non-turbo engine
only 6 INCHES of vacuum of 'reserve torque' in the engine means little hill climbing reserve