I've gotta tell ya,
I experimented a bit. The idle was a little rough so I checked and re-gapped my standard platinum plugs... lesssened the gap to .055". The idle was ok, but felt much weaker than the previous .060" gap.
Then I invested a whopping $13 in a set of copper core motorcraft plugs and set the gap back to .060"... I am more than pleased with the results! couldn't tell you how much horsepower gain, but the throttle response is a lot better when blipping for a downshift, it winds up a lot easier on acceleration from low speeds and top end acceleration is improved as I don't have to step quite as far into the gas to pass cars on the freeway.
for $13 and 30 minutes under the hood I can't think of a better investment.