Yes the GT2 compressors would be closer to the 63.5 but not as close as it sounds you were told. I didn't write down the measurements I took of my wheels, but the inducer was somewhere around 48-49mm? I think the GT2s are closer to the 997.1 Turbo vs. the 63.5 if we put them on a scale. Given your concern about the value of the car, if you did VTGs, I would use a 997.1 Turbo cores and leave your GT2 turbos alone.

Keep in mind like I said, my 93oct file was not all out, I actually told Sam lets not waste more time here lets go to e85 lol. I think you can get more, we just didn't try. I only use gasoline to store the car for winter. Check your vane positions that will tell you how bad it is on the stock compressor.

That 16psi run I think was bolt ons plus a tune (still stock turbos), not stock baseline run.

Other things in the system worth looking into, GT2s have the smaller intake manifolds, what exhaust are you running (catless?), the GT2RS intercoolers (what delta p do you have across them). And so on, plenty of areas to optimize. Biggest bang for buck is always what is in front of the compressor stage and what is behind the turbine stage, in between we can absorb quite a bit of evil in relation to the operating points of the turbo.