Unfortunately, I think you'll be in for some disappointment when you strap it down unless BMW has really bad mapping on those cars from the factory.

You cannot simply "add" up manufacturer's claims to come up with a peak power increase.

On top of manufacturers using numbers that are always enthusiastically high, gains from one modification to the other are rarely at the same point under the curve. One may gain the most increase at 3200 rpm, while another may add a small amount at 5800.

The end point is that you are happy with the changes and the way that the car drives, regardless of real number imrovements or perceptive differences. Dyno numbers at this point won't give you any real data to gauge gains.