Originally Posted by kickslop

Have you given the ECU a chance to add timing? Stop resetting it.

That's the only thing in the stock ECU you will seen gains from by only increasing octane, and if your timing advance was fine at your boost levels already, you're not going to see jack and will likely see a loss of power. Higher octane fuels burn slower. If you're not starting combustion earlier (through ignition advance, which you have zero control over right now), you have effectively just worsened your combustion events.

No Subaru is "tuned to" a particular octane.