Yes, you are trying to choose between a bunch of one-to-one (optional) relationships versus adding additional columns to a table all of which can be null.
I'd argue that neither option is "normal" (in the DB normalization sense).
So now the decision is one of how to denormalize. materialzed views and two ways to do so. The specific solution would depend in part on the final application queries that you need to write.
If you do want to model the de-normalized form, which I would likely be tempted to do given a fixed set of "events" that do not require additional related attributes, would be to place the few event timestamps on the main table and UPDATE them to non-null.
In the normal form you will likely find partial indexes to be quite useful.
David J.
Thanks David, my example was a big simplification, but I appreciate your guidance. The different event types have differing amounts of related data. Query speed on this schema is not important, it's really the write speed that matters. So I was just wondering given the INSERT or UPDATE approach (with no indexed data being changed) if one is likely to be substantially faster than the other.