I base my opinion on the final outcome. I see the TK's distribution of body parts or dumping of torso's as the thing that strikes me as the differentiating factor. For me it's the 'deal breaker.'
I genuinely feel that the way Jack left his victims was a vital part of his reason for doing what he did. As that aspect is absent from the torso murders I can't see them as the same person Whatever any similarities in knifework.
"There is nothing more deceptive than an obvious fact!"