If a row is in a page, and its varchar column is updated from holding 20 characters to 5000 characters, then it's going to cause a page split if the page doesn't have enough room to accomodate the extra 4980 characters.
That's correct.
What I'm saying is that the page split will not be on the PK, IF it is made into a non-clustered index. Page splits will potentially occur on the clustered index (or heap) of the table, whichever one that index may be.
The original question was about setting a fill factor value for the PK identity column. If that is made into a non-clustered index, setting the FILL Factor to 100 (or 0) should be OK. I don't see a scenario of page splits for the non-clustered PK in this case, do you? Unless I am missing something.
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