When your getting mapped, because the 2.5 will probably make more torque than BHP, You can get it mapped with preserving your Type R box in mind.
Main thing is not to blow your own box, that way you have it to sell to off set the cost of 6spd setup.
To keep the Type R feel you can always do what i did and get a DCCD 6spd
400 in Type r is good fun and even can be a handfull at times.
Its hard to get a nice balance between power and driveability, i have to admit myself that i had started to focus on the BHP figure and not consider its real life driveability, only wen i lately jumped back into standard Sti's and drove them as an every day car that i re appreciated what it was that made me love Subarus in first place, and thats the straight away power, no lag, power available like its on a switch not the wait ...wait... wait... HERE IT IS BANG power of a bad decision upgrade Turbo.
I know maybe i may come across as an SC embassador, but trust me im not im open minded and have no team jerseys of any company, but the Blouch Billet range they are selling seem to be truely great, some 400 turbos are spooling quicker than the standard Subaru ones, and the likes of an SC46 that has potential of hitting up to 500 but can have 1 bar at 2500 rpm to me is really an ultimate package, you pick the wrong turbo that can achieve 500 and the spool up could be near 1k revs LATER!!!,