2Many,
Well, the dual output coil is a single coil that has to jump two spark plug gaps because the gaps are effectively in series. If the gap is .030, then that amounts to a .060 effective gap to "jump". Once the gaps are breached, the effective resistance of the gaps decreases greatly, so the heat generated is higher and its the heat that ignites the mixture, not the pretty blue spark itself.
That's why all dual output coils are called "high performance". Not only do they have to produce a Voltage high enough to jump two spark plug gaps in series, but the positive Voltage spark plug requires as much as 40% more Voltage for the same efficiency as the negative wire.