I just removed the snorkel that goes to the outside of the car, it opened up the airbox alot more and made the car sound more aggressive, it sucks in warmer air, but it sucks in more air, keep in mind this method keeps the same filter membrane. Have a look on Ebay there is a Takeda intake that seems pretty good! This is probably the one I will get. I like the sound of the stock exhaust with the filter because it keeps the car quiet when you want it to be, and when you punch it it sounds a bit like a V8 ISF/ C63 to the novice ear :p I think the exhaust tone gives it a V6 commodore kind of element.
There much power gains from an intake, all it really does is add noise. The is250 doesnt really have much potential for power sadly, but it still handles quite nicely imo