Regarding the Speeds to fly on a DME-arc...
This depends on the class of aircraft.
First of all, the poster that claimed 180kts. is a max on a dme-arc is talking absolute rubbish. Don't follow his/hers advice unless this is explicitly mentioned on your plates. This will cause disruption to the flow and irritated colegues and controllers.
Doc 8168 "Aircraft Operations" by ICAO has a table which is quite clear...
For example: Class C aircraft: min. 160kts. max. 240kts during the Initial Approach , which includes most DME-arcs. By the way, max speed for visual maneuvering is 180kts.