I reran the code in msg312188.  Ints as before, string deletion +- linear up to 100 million, much better than before.

millions   old strings    new strings
of items  create delete  create delete
   4       1.55    .36     1.7    .38
   8       3.18    .76     3.6    .78
  16       6.48   1.80     7.3   1.71
  32      13.6    5.56    14.8   3.8
  64      28     19       30     8.4
 100      56     80       50    14.3