Scott this just isn't quite right on two points.
There have been several versions of turbos with different trim 71mm compressors and various turbines from 53mm to 56mm to 60mm turbines. (GT-RS, 2835, 3071wg, 3071 etc etc)
Mick's GTX3071 made less power everywhere than my GT3076 with the same tuner on 98 ron. Once Mick went to E85 the car was much more lively and definitely one of the nicest RB25 you would ever hope to drive (and it is a better drive than mine) however E85 would also give a similar leap in performance from my car if I cbf using it.
I do not believe the GTX is a step up in this frame.