400whp produces the same cylinder pressures whether you do it with 18psi and ported heads + cams or stock heads/cams @22+ psi. It doesn't matter to your pistons or rods. One benefit though is you turbo doesn't have to work as hard because your VE went up so charge temps would be lower and you would theoretically be further from knock.
I'd still throw some pistons in there though. I don't buy that nobody hones a block as good as Subaru crap.