I'm not sure what the power upgrade is, do you know what exactly is being done to get the additional 10 bhp. I have asked my dealer ona few occassions for details of upgrades however they appear to want to play them down. I'll assume that they don't mess with the warranty. I have asked about an axle back exhaust and they have said that they will have a look into it. I think they need to check with Subaru U.K. before suppling or fitting anything.