I have heard lot of ppl have had problems with the ignition, in regards to the EF. Myself included.
Apart from a dealer fitting the wrong plugs, I have changed these plugs to both NGK R (EF XR6 spec), and Spitfire plugs (EF-XR6 spec) !
I noticed absolutely NO DIFFERENCE between the 2, and considering that the splitfires cost me $14.00 each, and the NGK cost roughly $3.50 each, I will be continuing to buy the NGK R for now on.
I also fitted Magnacore 8mm leads, when the car was stuttering above 50Km, when it was floored. (the car wasn't pinging, the fuel just wasnt getting burnt).
I had original leads, and the wrong plugs at the time, and simply replacing the leads with the magnacores fixed this problem up immediately. (It was only when I was changing the leads, that I checked the plugs, and realised that they were incorrect, hence the purchase of the Splitfires.)
Mmmmmm. guess this story doesnt have a moral, or anything, just my experience with leads and plugs !