I think some of your numbers are based upon Stanley Gibbons cataslogue [perhaps, which has different numbers than Scott or Michel or Yvert.
To best sell a lot of stamps, wheth in lots of 5 each or any number, you will not get anywhere near catalogue. maybe 10% if that.
Sellking singley, as sets, or topical stamps (flowers, animals, ships, etc) could net you a higher catalogue percentage, amybe 50% or so, depending on the popularity of that stamp or subject.
Sometimes lots of mixed stamps sell for 5 cents per stamp.
Ir's a scary world out there on
ebay or Delcampe sometimes.
A good or better market for Bermuda stamps might be Great Britain or British Commonwealth countries like Canada or Australia or the Caribean Islands themselves.
To sell them here on Stamp Community (SCF) you need to read to Rules (button top right about number of posts needed, donations, etc.
A dealer who always sells caribean or British Commonwealth stamps would probably have knowledge of a greater customer base than others, and would be able to sell them on faster. Price paid is something no one can guarantee.