Although not directly related to this question, GT28R will not make near the HP of a GT28RS/GT2530. The GT28R has a 53mm 62 trim 11 blade T25 turbine wheel (same as GT25R), GT28RS/GT2530 has a higher flowing 53.85mm 76 trim 9 blade GT25 turbine wheel.
There is a ~12% flow difference in turbine wheels and 3% efficiency difference with the same A/R.