Ok, yeah, that was the problem. Changing one line of code gives:

0 words in a string gives an average of 385 comparisons. 1 words in a string gives an average of 374 comparisons. 2 words in a string gives an average of 366 comparisons. 3 words in a string gives an average of 349 comparisons. 4 words in a string gives an average of 342 comparisons. 7 words in a string gives an average of 294 comparisons.

With the same number of words counted in each string. Huzzah! It is now fast enough to run well on ciphers of about the size we're considering.