Not the same pistons but yes forged although I believe the 207 ones were stronger esp having a S202/203 or spec c. Reason why you're able to push more in a 207 is because it's a semi closed deck, and you can't as much on a 257 without sleeving it usually because its the same block bigger bore.

 

http://newenglandsubarus.com/forums/...ad.php?t=19548

V7 ej207: This motor is a direct swap for all 2002-2005 USDM WRXs. It is literally "Plug and Play" it does require you to purchase and install an AVCS harness

Benefits:
-AVCS (not offered in the ej205)
-Forged Pistons (not offered in the ej205)
-8250rpm redline (not offered in the ej205)
-Small Port Heads (not really a benefit... not offered in the ej205)
-IHI VF30
(460cfm at 18psi, 250-325whp, Bolt-On)
This is the standard equipment turbocharger used on the JDM V7 Subaru Impreza WRX STi. The VF30 is a thrust-bearing turbo that utilizes the P18 exhaust housing of a VF24 and the compressor housing sized between a VF23 and a VF22.
Expect to achieve full boost with the proper mods and a quality tune between 3000-3500rpms. 2002-2005 WRX owners will need fuel upgrades for this turbocharger and proper engine management is highly recommended for all vehicles.
-Semi-closed deck (not offered in the ej205)


Ver8 ej207: This motor is a direct swap for all 2002-2005 USDM WRXs. It does require you to purchase and install an AVCS harness

-AVCS (not offered in the ej205)
-Hypereutectic Pistons (not offered in the ej205)
-8250rpm redline (not offered in the ej205)
-Big Port Heads (not offered in the ej205)
-VF37 Twin Scroll Turbo (430cfm, 250-325whp)This is the standard equipment turbocharger used on the JDM V8-V9 Subaru Impreza WRX STI. The VF37 is a twin-scroll turbocharger that utilizes a thrust bearing design and a P25 exhaust housing. It is essentially a fast spooling VF30.Expect to achieve full boost with the proper mods and a quality tune between 2800-3300rpms. 2002-2005 WRX owners will need fuel upgrades for this turbocharger and proper engine management is highly recommended for all vehicles.
-Semi-closed deck (not offered in the ej205)

 

The only V8 STI blocks that had forged pistons were RAs. The non-RA motors are generally slightly less reliable compared to what we normally run thru stock STI blocks here.

 

I reedited my post to clarify.

I think the 207 block is a much stronger motor than the 257. Thicker cylinder walls, better cooling, and semi closed deck.

 

Thicker cylinder walls, yes. Oiling, yes (though the oiling system is generally regarded as a big weak point on all of the EJ207s across the board). Both are the 257 and 207 are semi-closed.

I edited my post right after you quoted it. EJ257s generally run slightly more power a little bit better than the JDM motor does. The pistons are still going to be what's holding it back.

 

With pros and cons depending on how you build the 257. Now with factory internals etc etc, definitely the 257 in the us is limited. While the JDM motor you probably aren't worried as much. Esp about cracked rings or pistons. Much better top end with the 207 also.