Cobb Tuning designed this 340HP Forester. Hopefully they will have these parts available for sale to the general public:
http://www.cobbtuning.com/oloa-fxt.html

Well right now you can get a 340WHP forester XT...

The GPMoto forester with a

GPMoto header
GPMoto Turbo back w single tip
GPMoto shortram
Unichip PnP
VF39
STi top mount IC

put down a shade over 350WHP.

340 at the crank, here is what I would do to hit that
GPMoto short ram
GPMoto header. (look Ma, no up-pipe leaks)
VF39
Unichip PnP or wait until the ECUtek is out for the XT.

Wow. Awesome.