No knocking in GDi engine because fuel injected direct just before ignition, whereas MPi fuel gets suck in and compressed before ignitionExactly!
If the engine is high compression, like 10:1 or above then you may feel just a slight benefit of ron97 but if not then it won't. It got nothing to do with being a new car or old car. I'm using Toyota Mark X with 12:1 compression, granted it's a GDI engine, but even with such high compression the difference between 95 & 97 is not really significant. No knocking when I use 95, fuel consumption also about the same, which means my engine has mapping for as low as ron95, so I just use 95 even though ideally in Japan use 98, not even 97.
As for turbo cars like your 4G93T, it should give more significant power increase if you turn up the boost higher! The higher ron allows you to achieve higher boost, that's the benefit. If not increasing the boost then will not feel anything la.