I've got a Mexi Strat that sounds a bit off if I tune to A=440, but one day I tuned by ear, listening for the least "wobbly" pitches I could find for each string and it turns out that guitar simply prefers to be tuned to around A=444. There is just more stability and fullness in the sound.
Of course there's all kinds of conspiracy theory surrounding the historical choice of 440, but in the end it's arbitrary. Certain instruments will naturally benefit from a slightly higher or lower tuning.
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