Usually the approach is to copy the formula. There are many ways of doing this, so it depends on the situation as to which is the best to use. It is also possible to select all the cells you want the formula to be in before you enter it, and then type the formula into one cell and press and hold the Ctrl key and then press the Enter key. The formula will be entered in all of the selected cells.
The superlative of efficient is "most efficient."
Spur Gear is the most efficient
More efficient and most efficient are the comparative and superlative forms of "efficient".
A screw is the most efficient.
ATP is the most efficient molecule
Heat is the most efficient agent of metamorphism.
most cost-efficient
Woodway Treadmills claim to be the most energy efficient.
more efficient, most efficient
Write-back cache is the most efficient when performance is paramount.
LEDs are the most energy-efficient lights as of 2016.
Some people mean the same thing when they talk about repetitive strain injuries and repetitive motion injuries. The difference is most likely that RSIs are from abusing a part of your body by working it improperly while a RMI is just from regular use.