The book that comes with the shiney bird I drive (B757) gives the figure of 3.5 miles per 1000 feet of altitude loss, this is at the economy Mach/ then IAS calculated by the FMS.
Interestingly...but not surprisingly..the whole thing comes down to energy management i.e. a heavier aircraft has more potential than a lighter aircraft, so at light weights we use 3 miles per 1000 feet, and at heavy weights we use 3.5 - 4.0 miles per 1000 feet. In practical terms, trying to match the desent profile is often impractical due to ATC constraints.
