Ideal % jump between gears?
Ideal differences are generally thought of to be around 15%.  Changes in excess of 20% make it difficult to select a proper gear for spinning based on varied conditions.  Changes of less than 10% are so slight that they will almost unnoticeable to most unskilled riders and even some skilled riders.  

You make an assumptions about the purpose of gearing on a bicycle that is incorrect.  Gearing is present to provide the proper gear to maintain a near constant and comfortable for the rider cadence in a variety of changing conditions.  They are not simply there to provide a shifting mechanism until the bike "gets up to speed".  A combustion engine has a power range that is most efficient at a certain RPM, but there is no comfort level involved.  It will produce any amount of power in it's range given the proper amount of gas. The human body does not work in the same manner.  There is a very defined range that riders are comfortable producing power in.  Generally producing power above that range causes drastic losses overall and can only be maintained for so long.  You miss the point that lower gears also need to be closely spaced to maintain that output in conditions that greatly slow a bicycle (hills, wind, etc).