Generally bigger is better for a TMIC, but you also need to think about flow. You can have the baddest TMIC in the land, but it wont do shit if youre not getting air across it. If youre thinking about upgrading, consider a new hoodscoop and splitter to accompany it (like the 02-03 STi scoop). No sense in getting a bigger TMIC if youre not gonna take full advantage of it.