I also developed a word search game and was interested in a methodology for determining what words are "reasonably findable".

The best I could come up without going through the dictionary word-by-word like you did was to use data from actual games played, to see what words were actually being found by the players.

Here is the word frequency from about 900 days of daily challenges (about 15 players per day), ranging from TEE found 4636 times to LAWYERED found once: https://docs.google.com/spreadsheets/d/1OY32E-JyHh2C4A_1ADy4...

In this game the goal is not completion but to get a high score that you can compare against others (and yourself from previous days). So far I haven't done much with the list of word frequencies except an experimental feature where you can see stats about your game using "commonly found words only", e.g. what percentage of commonly found words did you find.

You can try the game here: http://crosswordislandhopper.com/playGob And the daily challenge: http://crosswordislandhopper.com/dailyChallenge