Vacuum advance is an economy device - as you close the carb butterfly the amount of vacuum in the manifold increases, and the vacuum advance mechanism in the distributor advances the timing. Advancing the timing allows the engine to make the same power with less fuel but is very likely to have pre-ignition under any load... but when there is load, your foot opens the butterfly and the vacuum advance mechanism retards the timing again.
So, you can't get the engine to "perform" any better by playing with the vacuum advance, but you may get a little bit of fuel economy improvement
For reference, my engine runs well with 39° at full load (100kpa) from 2700rpm up, and 47° at full vacuum
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