I have tried from lowest and upwards with not much difference :-/
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Well they work, but won't drill as accurately as drill bits. In your place I would not rest until the problem was resolved.
It really looks as if even new drill bits are unable to penetrate your bass.
To me that indicates that they are being run too fast and quickly blunt. You have already learned to run your Dremel much slower. It helps to use some wax or oil as a lubricant, and use HSS drills, which do not get blunt when overheated. Dennis.