We already know statement-level INSERT triggers are faster than
row-level triggers in Postgres.
Out of curiosity I decided to time row-level and statement-level
INSERT triggers with a variety of row counts.
Here are the results:
Row Count vs Query Time
The takeaway here is that if speed is a concern, then you should prefer statement-level triggers to row-level triggers.
The scripts used to create the test database, run the tests, and generate the results are available in the companion GitHub repository.