Check
this thread out.
Basically and IIRC, and this I have no authority on so go to the source if it is critical, PANS-OPS defines a speed range for the various categories for various phases of flight. Your aircraft is certified for a given category, but if you for one reason or another cannot or will not maintain the speed range of that category for any given phase of flight, you must also upgrade your category accordingly and fly the procedures, minima etc for the speeds you are in fact using.
Rgds,
/Fred