My standard first three words; STROP, CHILD and MANGE cover off the 15 most used letters in English, except that the G should be a U, but I figured that if I've used the other four vowels and got no hits then a U or a Y is a given.
G is the 17th most used (B is 16th).
Therefore, when I've run those three words through I have a pretty good idea what the answer will be through a process of elimination.