Most big airports want you to fly 160kts to 4DME. On the 146 I fly we normally fly flap 18 (first stage of flap for those unfamiliar with the type) and gear up. At flight idle this give roughly 160kts whilst descending on the glide. Since our SOP's state we must have gear down and flap 24 at 4DME we normally take the gear at about 5 miles then flap 24.