A .005" difference in plug gap might be noticeable on an oscilloscope pattern as a slightly higher firing voltage with the wider gap. A clean plug firing from a squared-off center electrode will fire at around 8K to 10K volts, and the average point-type ignition system can develop 20KV or more. Once the gap is bridged by the spark, the voltage cannot go any higher, so clean plugs are the best option, regardless of where the gap is set. I really doubt that a .005" change in plug gap will make a performance difference during normal driving.

HEI and other electronic ignition systems can benefit from a little wider plug gap because they have a 50KV or higher voltage capacity and a wide gap allows more voltage to build up before the gap is jumped.
Jerry

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