[ormaaj]

This is totally uncomplicated. The choice of database is a function of your application and its architecture, not a matter of all-things-equal performance comparison.

"I want an extensible versitile database platform for use as a component in an infrastructure that is part of a larger system" - postgres.

"I want an embeddable lightweight SQL storage backend for a narrow scope, single-purpose, probably single-user, probably single-system application" - sqlite

Postgres should perform well in any role in the hands of an expert - it's a question of whether or not that is overkill. Sqlite can also perform well in a subset of those roles.