The less Ultimate influence, the better.
Thor and Don Blake are the same person, they're just filtered through different perceptions. They share the same memories, but they perceive those memories and their experiences differently. Blake is a man and perceives the world as a mortal, cosmically insignificant human being, whereas Thor is a god and perceives the world as a god. But each loves the other's world as much as his own--Thor longs for the euphoric bliss of a fleeting, mortal life where every second counts, while Blake is in awe of the cosmic and fantastical things Thor considers commonplace.
One of my personal favorite examinations of the Blake/Thor relationship is Jim Owsley's (a.k.a. Christopher Priest's) Thor: I, Whom the Gods Would Destroy
. It's one of the graphic novels Marvel put out in the '80s. I would highly recommend anyone who's confused about their relationship to check that out.