The GDI consumption will improve with the AR flash and a better manifold and cat.
I had the upgrade to manifold, cat and AR flash done just before Xmas. I've not gone through a full tank of petrol yet to test the MPG, but the early signs are good after a 70 mile run. I was getting 35 mpg pre the upgrade (at
allowable driving speeds!).
I must say, the upgrade has transformed the car. More responsive on the throttle and less sensitive on pulling away. The flat spot at 3000rpm has also disappeared. Nice sound from the twin pipes too! Expensive, but worth it.