The main Japanese depth charge, the type 95, sank at 6 f/s. The later Type 2 sank at about 10 f/s.
http://www.navweaps.com/Weapons/WAMJAP_ASW.htm
The Standard British Mk VII was also about 10 f/s. Later mods increased the sink rate dramatically.
http://www.navweaps.com/Weapons/WAMBR_ASW.htm
The Americans were about the same.
http://www.navweaps.com/Weapons/WAMUS_ASW.htm