OEM or equivalent. If you gain anything it's by replacing the worn out parts. The coil pack has more then enough spark for the engine & the plugs are basic platinum's & react better to the stock motorcraft or autolites.
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The Accel coil pack doesn't give any gains, it's just a branded 'performance' part. Some reports are that a few aftermarket 'performance' coil packs give a slightly smoother idle, but that's it.
You can get stock OEM Motorcraft coil packs online for $40-50 shipped, so they're usually the better deal if you need one. Otherwise keep the original on there.
NGK Iridium plugs won't add anything if that's what you're after. The iridium in them just makes them last longer, so they don't need to be replaced until 100,000-120,000 miles in engines they are spec'd for.
The new OE Motorcraft plugs spec'd for the 4.0L OHV V6 already incorporate the "finewire" design with a smaller electrode that was the big thing with iridium plugs, so new Motorcraft plugs will already give all the performance jump you can get. NGKs usually work better in Asian engines, the 4.0L OHV V6 seems to do best with the Motorcrafts.
Your big opportunity for performance is the spark plug wires. The stock wires are okay, but degrade and are really only good for ~60,000 miles. They'll last to 100,000 and beyond, sure, but new wires give a big improvement.
I suggest Magnecor brand, but anything that's good will do. What you DON'T want is gimmicky wires. Wires are wires, don't spend hundreds on junk that makes false promises. You just need regular 'ol spark plug wires made by a trusted brand name that makes solid, well constructed, reliable wires. Remember that they won't ADD anything that isn't there already, good wires just don't restrict the performance of the ignition system.
