The difference in vibe is noticeable to me - I would say that ISTJs are better at and consider facts to be more important. They are also more able to relate to people. Ask them how they feel about family and what their goals are, chances are INTJs want a good job (interesting, challenging, prestigious) and ISTJs consider it natural that certain limitations will be put into place such as staying somewhat close to family, job security...They can have a rad sense of humour (due to Ne?), but there's no Ni in there, they have little patience with the unconscious and sometimes fuzzy intuitive notions that drive the INTJ...they are not surrealistically absurd. They are more empirical than the INTJ and get more stuff done than the INTJ whose Ni/Fi can sweep them off track. Si-Te seems like a more natural combo than Ni-Te.
My ISTJ friend finds a lot of things that I don't consider established at all to be very self-evident.