I hit max boost with the SL55 last year at the track....that was before the 240 intake mani mod though...that mod dropped my boost down to 18psi....until I added the NW Dual CAI...
Both setups work very well.... I would have to say that the NW dual does flow better just from the smooter path the air has to take...
The reason I went witht the SL55 intake in the first place was that I did not like the looks of the single CAI in the engine bay. I figured the dual SL55 setup was at least as good as the single CAI and looked balanced. I would still be using it except for some fortuitous circumstances. I love the NW Dual CAI. It works great and looks great....

just my view...
I guess I could take both setups to the track and test them back to back.....