The version of the wrx that the U.S. got is version VII, the stock intake is a true CAI however it is very restrictive to cut down on intake noise. Removing the resonator will give you about 5hp at the wheels. The argument about CAI verses short ram, is pretty straight forward when looking at a turbo charged car, meaning that more air is better , a CAI is restrictive (long tube, lotsa bends) , sure the air is what 20deg. cooler but there is less of it and its just going to heat back up when its compressed. Suggestion is pay half as much for a short ram (pod, volocity stack what ever you call it) from HKS, or MRT, and upgrade to a better intercooler. If your MODS are properly installed your factory ECU can deal with up to about 260 hp at the wheels after that you will have to upgrade the injectors and that's when the ECU can no longer handle the task.

 

Sorry, 5hp at the wheels is wrong ,that should be 5hp at the crank.