As racing fuels go the only thing better than methanol is nitromethane blended with methanol to whatever strength the engine design can take. Methanol has higher knock resistance and burns more slowly than E85, for instance, all other things being equal. The stoichiometric air/fuel ratio of methanol is lower than E85, so more mass of methanol needs to be evaporated in the air prior to combustion - this means the evaporative cooling effect of methanol is greater than E85 for a given amount of air. This collateral charge cooling effect also influences toward greater knock margin and slower combustion.
An engine that is purpose built for methanol would employ higher compression ratio and/or higher boost pressure than an equivalent engine optimized for E85. A well designed methanol engine would have significantly greater knock limited horsepower potential than an equally well designed E85 engine.
Most likely the ideal spark timing for a fully optimized methanol engine would not be all that different from the optimized spark timing of a lower HP equally optimized E85 engine.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

I would suspect cyl-to-cyl variations in AFR. With very high fuel rates to is very difficult to get uniform distribution.
One reason that some people use two stages of injection, one in TB and the rest in injectors in each runner.
This is one reason that fuels with added oxidizers appear to be more tolerant.
I believe that HEMI is spot on, the differences in timing are largely to compensate for lack of optimization. I have seen similar numbers in other systems.

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P.E. Metallurgy, Plymouth Tube

Are you subscribing to the school of plug reading that affixes great importance to the change in color along the curved ground electrode ?