A WRX transmission will not hold near that power for an FYI. If you do by chance get the WRX drivetrain, you will have to upgrade diffs (w/e you feel like spending on them), a build 5spd, my gears were about $6500, a new clutch, flywheel, and then labor for that. So in the transmission alone there is 10K pretty easy. It does sound fun, and wish you the best of luck with the build. You did come to a great forum with a wealth of knowledge, I hope it helps you.
"2007 WRX- PPG'd, 20G- Tim Bailey tuned
Stage 2 2005 WRX