@Andrew: Do you know what the maximum boost is in your car, or, what pressure the waste gate is set for? If you can find that out, you can estimate the maximum possible power with this engine. Or you can calculate back from 0-60 mph times, or measure using something like the Torque App for Android and a OBD2 dongle. Any one of those methods will get you close.
Based on other cars I have driven, 40% more power will seem like a big difference on a normal road or in traffic. I personally would be thrilled to have that in this car.
The upper limit of power, before any losses, is the displacement of the engine and the amount of air and fuel that you can burn at a given rpm. After that, engine builders will size the intake and exhaust for the amount of air and exhaust gas. The goal in designing the intake and the exhaust is to keep the losses down to a minimum. The more boost you have, the more important the exhaust and intake become.
I suspect that you meant you use 98 RON in your car, which translates to about 93 Octane in the US.
Euro RON US Octane 90 85.9 92 87.8 95 90.7 96 91.6 98 93.5 100 95.5 105 100.2 110 105
From the video you posted, from the thread on NASOIC, and from my own experience, it looks like tuning for 93 octane or 98 RON gets you about 15% more power, at best, meaning at wide open throttle and high rpm.