The GT28 sounds like a normal 400HP turbo. Perfect for a CA18. The turbo in my avatar is a slightly larger GT28 with 0.7 compressor, 0.84 turbine. I can't tell you if that'll make any difference. My car is more for show than allround performance. That might change with time.
I think it will be a monster with the GT28. Turbos have gotten a lot better with the ballraced centres. Go for the newer technology, stay away from the T04.

i have gone GT28 turbo as my motor has had alot of work done 2 it 8000$ internals i chose the gt28 as it isnt as laggy as TO4 and is still very punchy very good alround turbo street and track.. i have had a TO4 on a mildly worked SR20DET was very laggy but once on boost went very well
GT series turbo's are a much better turbo. to as u can hear the compressor wheel which is (roller bearing)still spining. when u are out of your car! sounds wicked....

if u want a big turbo get urself a diahatsu copen turbo hahaha

Hey i have a ca18det in 1200 ute with big front mount, microtech fuelpums etc. Im currently looking at a turbo upgrade either To4e .58 exh housing, O trim turbine, 46 trim comp. wheel, .70 comp. housing, wet centre , 360 thrust bearing and external gate or gt28 rollebearing .64 exh housing, .70 comp. housing 54mm comp. wheel, 48mm exh wheel internal gate both cutom manifolds thanks for any help suggested