Something I have not seen mentioned so I will,,, 
Never go by the factory rating on coil voltage, many use a full 16.5 volts 
(Alternator level) off a heavy DC power supply to rate their coils.
Also spark-plugs have different resistance levels. So you have to 
match plug to wire to get the total resistance you want in the circuit.
Bosch are higher, NGK lower in general at a given heat range.
Gap affects the rise time of the coil, bigger the gap the longer the coil 
saturates because the resistance across the gap is huge until the mixture 
density and the spark energy reach the point an arc can occur. Higher 
pressure means higher voltage to bridge the gap.
In "the old days" we used a engine oscilloscope to see the spark 
discharge pattern during engine ignition. with it we could match gap, 
plug, wire,coil, distributor for best ignition. Not many mechanics use 
real scopes any-more...
Just some thoughts...
Dave