Turbos aren't all they're cracked up to be Paul, LOL . Only when they work?
WRX wagons are nice, you'll enjoy the burble again too.
It most definitely needs a remap Paul. You're right, just changing the backbox doesn't require a remap as it only really changes the muffling of the sound. Andy last mapped it when it was owned by Irish Al back in 2006, and I'll have put on larger injectors, uprated plugs, an up-pipe without a crack in it, bigger TD05 turbo and STi intercooler and undertray gasket. Should see around 330bhp or thereabouts when all done, but a huge change in the driveability .