OK, from page #198 in "Maximum Boost" by Corky Bell, he covers a twin turbo setup for the NSX (kinda neat that his book's test mules is an NSX, but I digress...)
In the book example, Corky is turbo charging a 3.0L NSX, by adding two aerocharger turbos running 5.2 lbs. of boost, with the goal being a 100bhp improvement.
By Corky's calculations, the Aerochargers would give 100bhp at 5.2 lbs. of boost. The formulat that Corky used for the performance gain comes out to [(275 + 100)/(275)] - 1, or .36. This is close to the math that Khuang originally posted, for the gain for the 5 lbs. of boost for the BaschBoost (note: that calculation is based on power changes, not efficiency).
The target cfm for Corky's turbos are 520cfm, split between two turbos. At 260 cfm, the flow map for the aerochargers show an efficiency of 58%. Looking at the specs for the Novi, the cfm is rated at 850.
Therefore, while the aerochargers max out on the NSX with a ballpark 100bhp gain, the Paxton, which I think is operating closer to it's peak efficieny (which I could not find on the Paxton site), since it's well under it's maximum of 850cfm at 5psi), loses less energy, and, therefore, can create more power...
Seem reasonable?
I am an interested party in all of this, since I'm on the list for a BaschBoost myself...