Hey for a NA motor anything is good. And if you have a CAI might as well put a flowstack on it to help it out. Better then wasting money on that useless electric supercharger. This is at least make the CAI more useful.
http://www.bpinitiatives.com/products.html#Graph_6 tahts their site with the graphs.

Here's an explanation from the guy who created it.
Far from equivalent. In fact you would probably be better off with a filter on than open ended pipe alone. A velocity stack benefits automotive applications for two main reasons.

1) Is the abillity to tweak and alter the air velocity profile and air velocities. Now this is a big benefit in ITB applications and various other racing applications, but as you did mention most of these benefits are dampened due to intake length and a plenum manifold.

2) The next major benefit is through the prevention of seperation at the entrance. The entrance of your intake can cause a significant head loss or loss of energy. These effectively creates a choke, due to the turbulent vortices and eddies created at the entrance. The severity of this head loss is dependant on the internal geometry of your filter, but can represent a significant "restriction". Due to the nature of turbulent flow, you cannot calculate losses analytically, but experimental data has been provided to correlate to. We can estimate head loss (ie. how restrictive) of the entrance geometry based on emperical data that exists. If we dig up head loss coefficents for plan ended pipe, square shoulder entrance and a radius entrance they are as follows: .78, .5 and .2-.04 (depending on radius) respectively. So head loss can be reduced by a factor of nearly 20 by running a stack over plan ended pipe.
Reference: Potter & Foss, Fluid Mechanics. Or you can run a search for head loss for viscous internal flow.
Interesting enough though, I just received some results from a customer with a 85mm B motor, that compared a Injen Velocity Stack Filter and the BPi Flow Stack. Gains of 2-3 ft-lb through almost the entire engine operating range. I will post us the result in the next several days or so.