Regardless, what is certain is that whatever tune was on this 997 GT2 previously GIAC crushed the numbers and improved upon it. The baseline on 91 octane with the 'competitor's' tune was 537 wheel horsepower. GIAC gained another 37 wheel horsepower on the same 91 octane fuel, impressive. On 100 octane this disparity grows to 148 wheel horsepower. Yes, huge.
The baseline tune was not tested on 100 octane however and it is unknown if they have a 100 octane map available so the 100 octane thrown into the mix skews the results. It is also unknown if the baseline tune was canned or custom dyno tuned. Based on the results, likely a cheap canned tuned. And if not a cheap canned tune then the argument can be made somebody overpaid considering what was left on the table even on 91 octane for GIAC.
GIAC shows significant prowess in tuning the 997 GT2 despite the issues this type of comparison presents. Mustang Dyno Graph below.