corpus: 589,025 words, 588,286 distinct 8-grams

arm                     gens  hit-rate  mean-longest   max
------------------------------------------------------------
base                     240      0.02           0.1    10
ckpt225                  240      0.13           1.1    11
ckpt300                  240      0.12           1.0    10
ckpt450                  240      0.13           1.1    11
ckpt900                  240      0.23           2.0    11

positive control (corpus slice vs corpus): longest = 160 (must be large, else the detector is blind)