i think you are talking about the procedural speeds given on the approach charts the speeds are as follows :
CAT A : 0-90
CAT B : 91-120
CAT C : 121-140
CAT D : 141-165
but let met tell you these speeds are the one which the controller expects you to fly from the Final Approach Fix not from the very IAF. Mostly in a DME arc to ILS approach you should fly at the IFR procedure Speed of your a/c for most cat C a/c it should be around 150kts but refer to the POH for the correct speed for your a/c.
