It appears that I was more interested in this that I thought, or maybe just wanted an "excuse" to avoid yard work.
As far as I can tell from the catalog specs, my shop vac flows about 325 CFM, although this could be wildly inaccurate.
Using an NA top on both the NA and RL bottoms, I measured a 2" WC pressure drop across both of them.
Using an airbox bottom with the resonator and inlet trumpet cut off I measured 3.5" WC with the NA top and 4" WC with the RL top.
All measurements were done with the same filter that showed some dirt, but a comparison test with a new out of the box filter gave the same pressure drop.
>The bottoms flow the same, and the inlet trumpet makes a big improvement in flow over a square hole.
>The NA top flows slightly better than the RL top, probably because of the shape of the exit. See the picture for a comparison, the RL is on the left.
Sky NA 2007 Midnight Blue
Sky RL 2008 Carbon Flash - Naked