I agree, I've been there before looking for those magic pub talking numbers, it's more to with drive ability and power delivery

 

There are a couple of bits of maintenance that can help with power delivery and response, such as cleaning the boost solenoid and MAF. Even on well maintained cars they can get overlooked, and they only take 15 minutes to do. However, they're not going to give you another 20 bhp.

Have you seen this:


I know it's not an impreza but it does show how
small jobs can make a difference.