sorry - wrong place
Oops, I meant to put this as a reply in the lexus cutting spark plug topics..sorry. Mod feel free to move.
The car mag I read was testing about a '90 Ford 5.0 V8. They tested before and after on a dyno (swapping in the aftermarket coil). Small net result in HP for an engine in the 300HP range - 75 or so above stock. So it was probably fine for stock and had a small inefficiency for the increased fuel flow.