Yeah, I was the one with the plugs !
I had $17.00(Each) Splitfires, and later changed them to
NGK R Plugs ($ around $3.00 or so).
I Honestly couldnt tell the difference.
(Both plugs were XR6 Spec).
The split fires need to be ordered from the agent in Melbourne,
where as the NGK R's are available from almost anywhere.
(I bought mine from Stupercheap).
Now for the leads,
I have magnacore 8.0mm Leads. (They have Stainless steel wire wrapped around a 2mm magnetised core). Compared to Silicon Suppressed Leads.
Before fitting the plugs, I had the worng spark plugs fitted by a Ford Dealer, and although it was OK for a couple of weeks, the engine started missing when I tried to accellerate it at about 50Km. Beleived it to be an ignition problem, so I went out and got these leads, and the splitfires.
Splitfires I had to wait about 2 weeks to get them in, but the leads were there already.
Whilst fitting the leads, I noticed that the plugs were wrong, (took them out for a visual check), and I noticed that they had pink colouration (Unburnt fuel).
Anyway, I changed the leads, but left the wrong plugs in.
The Car no longer had the above problem, and was running very smooth.
When I fitted the Splitfires, I noticed no further improvement.
Hope this helps.
P.S. My only suggestion with the leads is use small hands, and have a lot of patience. Do 1 lead at a time, and it should take you bout 1 hour to finnish the job !