I work for the world's largest automotive parts manufacturer, we've been making spark plugs for over 100 years. Yep, the founder of my company invented them. (Arthur Champion, AC spark plugs-AC Delco-Delco electronics-Delphi)

You won't notice the minute amount of horsepower gained from a spark plug,
and that gain is only if you were running fouled plugs to begin with.
Better starts, better fuel economy, smoother idle... sure!
7HP? Ask to see a dyno sheet. Not just the company's ad.