One thing is 100% sure - Oem IC must be upgraded on our cars.
Regarding power gains I don´t want to agree that it adds additional power.
IC upgrade will give us back some lost power (especially wheel power) what our cars will loose because of high IAT-s.
Regarding Simon MS ("they got +10 HP and 10Nm") - lets do not tell half of story, because they managed to get that +10 German PS on 4500rpm-s and they had + 11Nm on 6000rpm when car with oem IC, had 60-degrees of IAT-s.
German PS is not the same thing as HP or BHP. For example 300 German PS is equal with 295,896 bhp!
Run1 (with Oem IC): 292,0 PS @ 5550 rpm and 421,1 Nm @ 4120 rpm
Run2 (Forge IC): 300,0 PS @ 6905 rpm and 414,8 Nm @ 4230 rpm
It is clear that they got that total +8 PS just before rev limiter and it is only because of having cooler intake air temps (saved power).
More interesting fact is that because the total volume of Forge IC is so much bigger (it adds some turbo lag), they lost 6,3Nm in total. They managed to get 11Nm more torque on 6000 rpm but only because of lower IAT-s.