I can't remember where I read it, but when a violinist in the Vienna Philharmonic was asked about how to learn to be a great violinist, his reply was to listen to Fritz Wunderlich's recordings. I agree with that violinist (whoever he may have been), and find that the correlation between diction and right hand violin articulation is present on every vowel and consonant Wunderlich sings. And every time I hear his recording of the Dicterliebe, a recording I have listened to at least a hundred times, I am both overwhelmed and comforted.
Here is Fritz Wunderlich in "The Magic Flute."
And here he is singing Lenski's aria in "Eugene Onegin."
I have never been very good at math, but here's a violinist-tenor equation: If Fritz Wunderlich = Michael Rabin, then Richard Tauber = Fritz Kreisler.
Who would balance DeStefano, Gigli, Caruso? and Bjorling? Any suggestions?