i own both the evo X GSR and my05 wrx. based on my personal experience .i would pick the mitsubishi anyday .as monitored and compared , my fully stock subaru gave me about 8km/L on 60% highway drive and 40% city driving.but my evo with just the kakimoto exhaust and arc intake gives me close to 9.5km/L on the same basis .
i am not really a very technical person but given my experience on the road and also my butt feel , evo generally gives a nicer drive interms of handling with all the computer techs whereas the impreza gives you a more raw handling experience.so it all boils down to which you prefer.
and oh ya , if comparing stock and stock , the evo 8/9 is definately faster than the version 7/8/9 sti on straights and around the corners.evo comes with slightly bigger turbo as compared to the IHI vf series that subaru offers.given the fact that the evo engines are generally stronger than that of the subaru boxer , it is safer and easier to achieve bigger hp figures at a lower cost .and due to the engine placement of the subaru boxer , you will realize that they actually ultilize the top mounted intercooler setup instead of the fmic .changing to a bigger turbo and fmic setup with a impreza and you will experience the ultimate lagness cos of the intercooler piping setups.and by the time you get really fussy about it , here comes the reversed manifold setup which again , dials in more and more cost.both are great cars i would say , but personally i think the evo is cheaper to maintain on the long run and have better dollar to horsepower ratio .
just my 5cents worth.