I've read that most scoobies have more power than quoted from the factory. Is this true - and what's the reason?

 

This has been discussed many times, without any definite answer.

I do believe Subaru did put the engine on a bench dyno, where it produced 218 BHP (MY99/00)

The rolling road of preference 2 years back was consistently giving higher numbers (230 -235 bhp), whereas others sometimes even give less on stock cars (210 BHP). See dyno pages (link on top of this page)

I believe it is hypothetical anyway... on a good cold damp night, an Impreza may produce up to 20 bhp more than on a dry hot summer afternoon.