That is the problem I have with the 4nm and 4,5 mins. I simply cannot see it descending with 60kts at a rate of 6.000 ft/min. At 60kts (~30kts IAS at altitude) the required lift for that RoD is not there.
Henra, did you forget the vertical component of velocity? They add vectorially. And as the velocity vector is largely pointed down, drag (which is substantial) helps support much of the weight of the aircraft.