Any bolts where you're principally concerned about strength should be 12.9, but needing 12.9 bolts on a bike is really an indication that the fastening has been designed wrong and should have more/larger/differently disposed fasteners.
@gbj_tester started
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Any bolts where you're principally concerned about strength should be 12.9, but needing 12.9 bolts on a bike is really an indication that the fastening has been designed wrong and should have more/larger/differently disposed fasteners.