Best possible mileage?

Setting the optimal cruise advance was one of the changes I made with the headers, carb, head, and thermostat. I'm wondering if the BBD is just operating leaner out of the box than the original Holley 1945. The plug on the left was before the mods and on the right is now...
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I should have added that after setting the timing for cruise, the idle timing went from 2 1/2 deg - factory spec to 11 deg BTC.