Bill,
I would only advocate bigger plug gaps, & always have, like 060 with a powerful ign system like HEI. Would not recommend it for stock Mopar system, never have.
If I am reading your post correctly, the engine that got smaller plug gaps was turboed. Not surprised at all it misfired with large plug gaps. Pretty sure I said earlier in this thread [ could have been another thread ] that bigger gaps like 060 are for NA engines. Non - NA such as turbo, blown, nitrous are likely to misfire with 060 gaps HEI.
The benefits of bigger plug gaps may not be felt or measured at higher/peak rpms but are often felt at rpms other than peak. People with thick heads do not understand this. Comments like 'Increased the plug gap & engine runs smoother'. That means it is misfiring less & making more HP, but only felt at cruising RPM.