I forget which of Rutherford's books it was but one of them had an advertisement, in the back, for his collection of the 'rainbow' series books that said that you can learn more from 15 minutes of reading his books than a lifetime of Bible reading.
If someone with access to his books can hunt that down it would make for a devastating quote.
By the way, I recall reading in one of the editions of The Harp of God that Russell was the 'Faithful and Discreet Slave' (Probably phrased slightly differently as they would not be quoting from the NWT). The book went through several changes in subsequent editions so I'm not sure if they all say the same thing.