most folks don't understand that the difference between 4.8s and 5.5s is "less than a second"....on a 1/4 mile strip, that means a lot but on I-75, it does not......
I think this is such a valid point. If you intend going racing, you need to chase the numbers, each fraction counts. But in the 'traffic light grand prix', it can be as much about the driver and reaction times as anything else.
I fully understand your desire to tune the car you have, but I don't get the need to try and match the GT (GTS here in UK). I have a diesel model and will look at tuning that, but I wouldn't even consider trying to get to GTS or even 2.0T levels of performance. It may be possible to match the 2.0T, but I drove and could have bought a 2.0T, but the right car for me was the diesel. High petrol costs in UK and high annual mileage.
You chose the car for a reason, just make it the best car for you. That is what I intend to do with mine.
You can also take a different approach. If you want to have the fastest 2.0T, weight reduction is as good as power increase and helps with handling too!