When it comes to fuel burn, in terms of air nautical miles per Lb/Kg most aeroplanes are MORE economical with one engine shut down.
This is probably to do with two factors: Running the remaining engines at a more efficient (higher) RPM and cruising at lower speeds, and therefore creating less drag.
Worth checking the perfomance manuals on this one, chaps.
And speaking from personal experience, I can categorically state that the VC10 flies quite well on two engines - even if the two which are shut down are on the same side!
I wouldn't want to get airborne on two, but it gets off the ground on 3 quite nicely.