I'd go for the 5.5Ø
5.0 is the tap drill for M6×1.0, if you drill 5.5 you'll be cutting away the bits of aluminium which are holding most of the load.
That's a better call than mine.
@JurekB started
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5.0 is the tap drill for M6×1.0, if you drill 5.5 you'll be cutting away the bits of aluminium which are holding most of the load.