Spark plug gap is conditional on how much total energy the ignition coil puts out. Energy, not voltage. The wider the spark plug gap the higher voltage needs to build up to ionize the fuel-air mixture in the spark plug gap. Once the mixture is ionized current can flow across the plug gap. The time the current is flowing across the plug gap is the burn time. Typically, 1 to 1-1/2 milli-seconds.
All else being equal, the more voltage it takes to ionize the fuel mixture the less energy is available to sustain the burn time, and vice versa. The less voltage required to ionizer the mixture the more is available for burn time. You want enough burn time that the fuel-air mixture in the combustion chamber is exhausted.
Obviously, the fuel-air mixture plays into this as well. A richer mixture in the plug gap is easier to ionize. You can see that there are multiple variables involved. So, it depends.
