I have a 320bhp STi and it's really economical (have rarely had a hugely economical car, so to some it may not be, but for the performance it is). Always over 30mpg on a decent run, mid 30's if you really want. Obviously if you're gunning it, and you will want to some of the time, that figure will drop dramatically, but at sensible revs it's brilliant on fuel for what it is.

It is mapped on V-Power though and I never put anything else in.