The Port size of the STI and the EJ205 is about the same. But the Combustion chamber is much smaller on the 205 heads. If you likeTrq the 2.5 is the only way to go. Its 25% larger and has a much higher power potential. But it has its disadvantages. It drinks ALOT more fuel. It took 5-6 miles to gallon right of my car the minute I put it in. They dont like to rev out, they sound harsh doing so.
To me... A V8 EJ207 with Twin scroll and a JDM 6mt is just Heaven. The sound, feel and power band matches the car.