Yes I have that issue also. It seems the throtttle has too much authority over airspeed and the descent angle not enough. In the 727 we reduce thrust to in flight idle and decend at our chosen FPM. If you bring the trhust levers to in flight idle in the CS727 you airspeed will drop unrealistically. It's not very accurate.

But you shouldn't be slowing to 250 kts at FL300. You should start slowing in tiem to pass 10,000' at 250 kts.