This should not have to be as confusing as it would appear to be, at least I do not think so!!
1) Production International Spec. 2.0 Litre Sti Version 7: Forged Piston, as per photo, in handbuilt short.
2) Production JDM Spec. 2.0 Litre STi Version 7: Forged Piston, as per photo, in handbuilt short.
3) Production International Spec. 2.0 Litre STi Version 8: Forged Piston, as per photo, in handbuilt short.
4) Production JDM Spec. 2.0 litre STi Version 8, TypeC and Type RA: the latter two at least are using the forged piston as in photo, if not the base street car as well. There are Japanese market reasons why they MAY have gone to cast pistons in the street car, which have NOTHING to do with strength and everything to do with new emissions regs which came into force in that market at the beginning of 2003.
5) Production USA Spec. 2.5L STi : cheap( $80 each), cast piston, as per photo, in mass production short.
The piston pin alone, as an example, indicates the difference in the durability of not just the piston, but the entire short. The 2.0L STi short features a tapered bore work of art. The Forester 2.5L short uses a conventional parallel bore mass production piston pin. We have tried to show this in our photos , however it is difficult to show accurately, sorry. The differences flow through every other part of the short, including the PISTON!
Just as an aside, for those of you with the experience to appreciate this fact, check the production clearances the STi version 7/8 forged piston runs at: 0.0004" to 0.0012 !!
On a bore in excess of 3.5"!!. Try THAT ( well actually, no, please don't!!), on your typical aftermarket forged piston!
Now , to be fair, when we are going to really lean on them, or road race them, we do increase the clearances to just under 0.002". However, still, this would be around half what you would typically have to run on a quality aftermarket piece. The current STi 2.0L forged piston, ( which is VERY different to version 6 and earlier), is truely a work of art! We cannot speak highly enough of them!
We just wish there was an equivilent for the 2.5 L engine, however, there isn't.
Now, I hope I have explained this clearly enough!