I picked up a set when I was trying to debug an idle problem. In the end the idle problem was a broken flame trap. Anyway, on a long highway trip in back to back tests against a Bosch Super plug, the +4s seemed to give me a 0.5 MPG increase. Of course factors like weather, speed, and even fuel quality can also bump your mileage around by even more than that. I think the conditions were reasonably similar when I did the compare.
Right now the Supers are back in and I will use the +4s after I get some more wear on those.
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