What are physical differences between both to spot on the sight?
Other than that, what are technical differences?
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According to this article in Wikipedia:
that refers to this other page from Ken Rockwell:
the only technical difference is a different IS algorithm that recognizes panning.
Technically, there is no difference - optically, they are exactly the same.
Given the above, it doesn't matter to much, but original has a silver band round it and the II version doesn't.
As an aside, exactly the same applies to the 55-250 as well.