ct12a steel wheeled and high flowed is a now completely different turbo to a stock one so not surprised they can make that power
same as a ct15b on a vvti 1j stock they have full boost at 2500rpm but are restrictive up top once highflowed they can make around 300kw if done right
as any upgraded turbo ,which would cost the same as a new turbo anyway so may as well just pick a new one using
compressor mapping ect for the engine .
not saying ct12a is a bad turbo just think there would be better alternatives