There might be more then one.
In class D airspace for IFR aircraft the 250 max speed applies irrespective of ATC suggestions or needs.
In case 250 below 10k is written on your OM-x, depending on the wording, it might be legally binding with same effect as the above.
Is there an AFM limitation for the aircraft model?
Though I understand your question and possibly theirs too was aimed at the communication CRM tools, and how to apply them.