I found that on my old r33, I did have a high flow K&N in the stock box, but I picked up a pod for like $25 with everything to bolt it on.
I didnt have a cold air intake box, the pod just sucked air from the engine bay.
I didnt see any difference by just swapping, other than lovely intake suction and bov whoosh noises coming out of the pod.
I would think that a pod with a proper cold air intake setup with proper vents to allow air to flow through to it would probably be great on the track, but for everyday use I wouldnt think there would be much difference between a high flow panel in the stock airbox or a pod in a CAI setup....?