I just bought a MY07 tb STI bit over a week ago with 63,000kms
Trip computer hasn't been reset in a while and fuel consumption is 13.6L/100kms over the last 8000kms. The car was owned by someone in Melbourne (serviced @ Subaru Docklands + Mentone) so I'm guessing unlikely to be mainly country kms.
When I fill up (twice already - been driving a lot and hammering in S# when possible) it says 550kms til empty. I think 550 is optimistic, but 450 doesn't seem unreasonable.
Only thing which drops it for me is driving cold and take-offs. Once warm it cruises between 2L - 10L most of the time. I think Intelligent mode may be more fuel taxing than S# as it requires revving a lot higher to get moving at the lights.
Not sure if mine has any mods. A tune / dump pipe is possible, but I have no idea.
it does have 2 stainless cat back canons on the back with twin 2.5-3" pipes, but they're very quiet and only make a bit of a nice sound over 4000RPM. There was a brand underneath which I didn't recognise - may have been Japanese?
I wouldn't mind getting more noise out of these (without modifying much) if anyone reading has ideas.
Car goes really well - smashed a newish Golf GTI the other day before I was familiar with the car (never owned a turbo before and haven't had a manual in almost 10 years). Despite losing he had a huge grin on his face