[350TSS]

Luddite: I think someone is trying to sell more expensive iridium plugs - surely the coil delivers its designed voltage because that was what the designer of the coil and the manufacturer had a spec for.
The ability of the electric charge to jump the gap should be a function of the pressure in the cylinder, the density of the fuel mix in the combustion chamber, the time the coil has had to recover from the last discharge, the temperature of the cylinder head and the position on the prescribed advance curve and the cleanliness /conductivity of both sides of the gap.
The voltage at the side of the gap from which the spark starts to jump will be what the designer/ manufacturer specified regardless of the thickness of the electrode. This may or may not be enough to jump the gap depending on the circumstances above.
I suspect a bigger gap is harder to jump than a narrower one, think about striking the arc on a stick welder.

I also wonder if a long thin spark ignites the fuel better than a shorter thicker one.

You can tell I am a bit bored. Let's have a debate and we can all talk boxxocks about subjects we (particularly me) know hardly anything about