Here's my results with spark plugs... The whole story.
A friend (Henceforth called Alex) told me he put in new spark plugs, and his car gained a whole bunch of horsepower! He got the top-of-the-line Platinum +4's... He said I should do the same. I told him I don't think +4's actually made much of a difference, if any. Now, then, much deliberation ensued, and I put him up to it; 'Alright... Here we go... I'll buy three sets of spark plugs. Iridium, Platnum +4's and stock Denso's for the Protege, and test all of them on my GTech (Go ahead and laugh at me. =)) The conditions, in order to be the same, were predetermined. Run the car for half an hour before hand to even out the adjustment for heat soak, and run on a road adjacent to a Mobil station, refueling with 87 octane after each of 9 runs, three runs on each plug. His end of this deal was as follows: He would pay for each set of plugs, and buy me dinner if I saw more than a 2hp gain from swapping the plugs. And I would buy him dinner if otherwise, and soak the loss from the plugs. Sounds like a good deal to me!
Alright, onto test day. Like I said, I refueled after every run, to make sure the weight of the car and the draw was consistant. FYI, my car returns a more or less solid 114hp from the GTech. I pulled into the gas station, and changed to the Denso's first. I'm getting really used to changing these damn things. Checked everything, topped up the tank, and off I went after dialing the weight into the GTech.
Denso Results:
Run 1: 114hp
Run 2: 114hp
Run 3: 114hp
Nice and consistant, as I expected. Then I went to the Bosche +4's. This is what I got from them; The revving was smoother, and steadier as I got into the higher revs. And this is what the GTech showed me:
Platinum +4 Results:
Run 1: 114hp
Run 2: 115hp
Run 3: 114hp
And, I installed the Iridium's last, and did another set of runs. This time, the plugs allowed for a lot smoother revving all along the range. Here's the results:
NGK Iridium Results:
Run 1: 114hp
Run 2: 114hp
Run 3: 114hp
As you can see, there's no real difference according to the infinitly accurate GTech meter.

I got a free dinner, and a few sets of fresh spark plugs. Not one to be a jerk about that sort of thing, I paid the tip at dinner, and soaked half of the price of the plugs.
OH, and 1st? My Sparkco plug wires didn't break on me at all. =) I was totally psyched! Hehee.
Here's the summary with averages for those who don't care to read:
Denso: 114hp
Bosche Platinum +4: 114.3hp
NGK Iridium: 114hp
Enjoy.