Sorry but your history is
Sorry but your history is wrong, they never "switched" to cast pistons, the 2.5L never had them, and neither did the 2L wrx's in 02-05. It was never Subaru's plan to use the EJ257 in the STi in US/Aud markets but they were unable to get the EJ207 to pass emissions during cold start because of the forged internals, so they went with the 2.5L.