Go as low as you can, just make sure you have enough vertical wall on the inside for your SS washer. And, actually it is best to drill fast with aluminum, at least with regular bits ( you want to drill with speeds less than 700 rpm with steel). Check out a pneumatic drill designed for AL, they spin at 2,600-6,000 rpm.
I used to be dyslexic, but am KO now!!
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