^^^What Dave said...

SLK320 = cosmetic upgrade only.

C320 = cosmetic AND a slight horsepower gain.

Needswings is still the best route to go for max HP, as it replaces more components at once and makes a much smoother/straighter shot from the inlet to the intake manifold. The C320 box is just shy of a NW single... but I chose it for aesthetics because I'm not fond of the big gaping hole on the side of the O-Shaped ML320 cover that is often used with the NW single. Green Ghost did a superb job of filling in the said gap... but it's not an every-man mod. If I ever get around to finding and modifying the ML320 engine cover to my tastes, I'll be upgrading to NW.

The MAF and throttle body alone will almost cost as much as a NW single, and still won't flow as well. BUT, we're talking an N/A Crossfire, and I can't see the difference being much more than 2-5 RWHP between my current setup and the NW single.

It's all in what your end goal is...