1万件のインサートで、素のハッシュマップの場合、Valueのサイズが120バイトならばBoxに入れる価値が大いにある

small(40バイト)
test indexmap::initialize_performance_test::tests::bench_init_hash_map_fast             ... bench:   1,376,222 ns/iter (+/- 24,219)
test indexmap::initialize_performance_test::tests::bench_init_hash_map_fast_with_2boxes ... bench:   2,030,002 ns/iter (+/- 16,896)
test indexmap::initialize_performance_test::tests::bench_init_hash_map_fast_with_box    ... bench:   1,432,410 ns/iter (+/- 8,569)
test indexmap::initialize_performance_test::tests::bench_init_hash_map_slow             ... bench:   1,632,320 ns/iter (+/- 38,289)
test indexmap::initialize_performance_test::tests::bench_init_index_map_fast            ... bench:   1,601,450 ns/iter (+/- 16,388)
test indexmap::initialize_performance_test::tests::bench_init_index_map_slow            ... bench:   2,019,440 ns/iter (+/- 33,851)
test indexmap::initialize_performance_test::tests::bench_init_linked_hash_map_fast      ... bench:   1,610,930 ns/iter (+/- 11,677)
test indexmap::initialize_performance_test::tests::bench_init_linked_hash_map_slow      ... bench:   2,031,240 ns/iter (+/- 91,206)
test indexmap::initialize_performance_test::tests::bench_init_str_vec_fast              ... bench:   1,466,270 ns/iter (+/- 12,675)
test indexmap::initialize_performance_test::tests::bench_init_str_vec_fast_with_box     ... bench:   1,619,870 ns/iter (+/- 19,395)
test indexmap::initialize_performance_test::tests::bench_init_str_vec_slow              ... bench:   2,024,020 ns/iter (+/- 20,202)
test indexmap::initialize_performance_test::tests::bench_init_str_vec_slow_with_box     ... bench:   1,905,420 ns/iter (+/- 10,927)

big(120バイト)
test indexmap::initialize_performance_test::tests::bench_init_hash_map_fast             ... bench:   2,852,437 ns/iter (+/- 37,721)
test indexmap::initialize_performance_test::tests::bench_init_hash_map_fast_with_2boxes ... bench:   3,144,620 ns/iter (+/- 361,220)
test indexmap::initialize_performance_test::tests::bench_init_hash_map_fast_with_box    ... bench:   1,634,070 ns/iter (+/- 41,234)
test indexmap::initialize_performance_test::tests::bench_init_hash_map_slow             ... bench:   3,808,910 ns/iter (+/- 100,621)
test indexmap::initialize_performance_test::tests::bench_init_index_map_fast            ... bench:   2,094,885 ns/iter (+/- 79,610)
test indexmap::initialize_performance_test::tests::bench_init_index_map_slow            ... bench:   2,532,350 ns/iter (+/- 57,005)
test indexmap::initialize_performance_test::tests::bench_init_linked_hash_map_fast      ... bench:   2,234,780 ns/iter (+/- 218,209)
test indexmap::initialize_performance_test::tests::bench_init_linked_hash_map_slow      ... bench:   2,652,150 ns/iter (+/- 124,200)
test indexmap::initialize_performance_test::tests::bench_init_str_vec_fast              ... bench:   2,125,645 ns/iter (+/- 12,427)
test indexmap::initialize_performance_test::tests::bench_init_str_vec_fast_with_box     ... bench:   1,837,690 ns/iter (+/- 24,682)
test indexmap::initialize_performance_test::tests::bench_init_str_vec_slow              ... bench:   2,962,080 ns/iter (+/- 50,469)
test indexmap::initialize_performance_test::tests::bench_init_str_vec_slow_with_box     ... bench:   2,116,910 ns/iter (+/- 56,773)

10件の場合Boxに入れる価値はないです(120バイト)
test indexmap::initialize_performance_test::tests::bench_init_hash_map_fast             ... bench:       1,356 ns/iter (+/- 22)
test indexmap::initialize_performance_test::tests::bench_init_hash_map_fast_with_2boxes ... bench:       1,941 ns/iter (+/- 13)
test indexmap::initialize_performance_test::tests::bench_init_hash_map_fast_with_box    ... bench:       1,481 ns/iter (+/- 6)
test indexmap::initialize_performance_test::tests::bench_init_hash_map_slow             ... bench:       1,992 ns/iter (+/- 16)
test indexmap::initialize_performance_test::tests::bench_init_index_map_fast            ... bench:       2,051 ns/iter (+/- 27)
test indexmap::initialize_performance_test::tests::bench_init_index_map_slow            ... bench:       2,824 ns/iter (+/- 16)
test indexmap::initialize_performance_test::tests::bench_init_linked_hash_map_fast      ... bench:       2,234 ns/iter (+/- 5)
test indexmap::initialize_performance_test::tests::bench_init_linked_hash_map_slow      ... bench:       2,701 ns/iter (+/- 10)
test indexmap::initialize_performance_test::tests::bench_init_str_vec_fast              ... bench:       1,576 ns/iter (+/- 3)
test indexmap::initialize_performance_test::tests::bench_init_str_vec_fast_with_box     ... bench:       1,799 ns/iter (+/- 20)
test indexmap::initialize_performance_test::tests::bench_init_str_vec_slow              ... bench:       3,146 ns/iter (+/- 42)
test indexmap::initialize_performance_test::tests::bench_init_str_vec_slow_with_box     ... bench:       2,578 ns/iter (+/- 104)