The short answer is that there is no detectable difference on the dyno.
The long answer is that the flame front propagation speed is pretty fixed. It is kind of like the difference between starting a gasoline soaked bonfire with a match or a lighter with a 2 inch flame.
A bigger broader spark may act like slightly advancing the timing, which does improve performance, but like I said we couldn't measure the difference. I suspect that simply replacing old worn out plugs improves performance : )
Thanks! That makes sense.