looks like we are thinking alike on this:
The most common definition of "material" I have seen states that a fact is material if "there is a substantial likelihood that a reasonable shareholder would consider it important" in making an investment decision, or, stated in different terms, the fact "would have been viewed by the reasonable investor as having significantly altered the 'total mix' of information made available." This oft-quoted language is taken from a 1976 decision of the U.S. Supreme Court (on page 449):
I think a 5-10% "effect" would be considered as a reasonable threshold to the "total mix".....of course, lots of this is hard to put a definitive number on......
PS: good links, thx....