I get the feeling that 'thou' is the more formal because Hemingway uses it in For Whom the Bell Tolls to reflect the formal aspect of Spanish. But I'm not too sure about 'thee'. I give you "Let me lay waste to thee" from Wolf Like Me by TVOTR, which is obviously using it to refer to a person. Are both nominative? Are the two interchangeable?
Oh and morning all. Is this too early?