You are mistaken. The E89 30i already has a 3 stage manifold. The 30-40 horsepower increase (which is true) comes from upgrading a 3.0i (with single stage manifold) N52 as used in the US-spec post-LCI E85 and swapping in the European-spec 3.0Si (three stage) manifold.
The 3.0i N52 was never fitted to UK E85s. The equivalent modification is upgrading the 2.5i N52 to 2.5Si.
