Get the 2.5XT and have it tuned at some place like Orange (EcuTek) or Autoplus.

In stock form Subaru's 2.5li turbo engines seem to run very rich (obviously for safety against bad gas). If you're diligent enough to run only high-octane Blaze or V-Power, a retune will not only get you more power, it'll also give the car much better economy.

A friend of mine has had both his STIs tuned at Orange, I'm still putting some more miles in my car, but eventually i'll get my rex tuned there too. HTH