Have recently been looking into this myself and my interpretation is as follows - If the DME arc forms part of an initial approach procedure, PANS-OPS promulgates the acceptable speed range dependent on the category of aircraft that the procedure is designed for, or restricted to. (Cat C 160 to 240kts). While the procedure design does allow for winds aloft to affect the ground track, PANS-OPS also states that for this type of procedure, you only get the full 984ft (300m) of terrain clearance within 2.5nm of the DME arc centreline and so in some conditions, lower speeds may well be advised to remain within this area.