You're going the wrong way for boost. 22 heads on a 25 block gets you high compression with poor flowing heads. Decent low end for off-roading and such but bad for boost.
I can personally attest that a 22e bottom end with 25d heads will LOVE some boost if you can tune for it. I ran 18psi from a td04 for a while in my coupe, it was a blast.
That said, if you're dead set, sti (257) is the best you'll get from Subaru, after that you're gonna spend serious coin on an aftermarket block with forged internals, closed deck, etc.