Port Seton.
About £500 - £600 bargain for the remap.
The exhaust is the best way of releasing power - full decat or sports cat (as I said above).
Remapping on the standard exhaust is a waste really as you can get more with a change. You're looking at circa 275 BHP with an exhaust change and map but the torque will match this. It's overall driveability you need, not just BHP. PPP is the other option but more expensive. Andy could get you more as he has on his own cars BUT the engine and its components (not least the gearbox) will be under strain.
These cars can be fragile if badly modded, can det and essentially fail so you need a quality map by a guy like Andy to make sure you still have a car that runs. Would NOT recommend a superchip as it may be cheaper and good for a saxo but not for an Impreza. Issues like fuelling and timing need to be carefully set for your car and for your mods, not just a general model map.
Gonna cost you around £1000 to get a good map, full exhaust system and maybe a uprated hoses in the engine bay. You'll want to get a knocklink to see if its detting (very bad) and maybe some other gauges to make sure it is running well. Andy would map it for Optimax.
Brian