efficiency results in one thing: more stuff for the same cost as before (or put another way the same stuff as before for less money). And yes, this is definite

efficiency results in one thing: more stuff for the same cost as before (or put another way the same stuff as before for less money). And yes, this is definitely knowable because the one thing efficiency results in causes a wealth effect for all consumers (and/or a wealth effect for capital owners to the extent they can capture the gains from efficiency vs having them competed away causing lower prices and a wealth effect for consumers) and a negative income effect on the subset of workers no longer needed because of the efficiency gain. For an efficiency gain to not cause a GDP increase eventually the income effect has to swamp the wealth effect for all time, which has never happened and is unlikely to happen any time soon, as there are no signs of any abatement in consumption demand that would cause a wealth effect to not cause a consumption increase (this is especially true given the incremental nature of efficiency improvement implementation over time primarily because of various productive limitations on adopting new tech. The more time people have to grow into a higher consumption state the more likely and easier it happens.)