I have tried stock paper, K&N, and Amsoil 2-stage foam on an S70 and a 240. I doubt any of these will make any appreciable difference in performance, especially on a non-turbo. On my turbo, the weather makes more of a difference than any filter. However, in this application, the K&N does seems to provide for slight better throttle/turbo response, but I have no quantitative basis to support this (in other words, it could be in my head).

If you get either a K&N or Amsoil filter, you need to realize on thing - these are reusable filters and you are signing yourself up for the periodic cleaning ritual. It is much less work to just pop in a clean paper filter. In terms of the cleaning and re-oiling ritual, I think that the K&N will have the edge. I found the Amsoil foam to be a real pain in the wazoo and ended up tossing it back on the shelf. But, that's just me.

In terms of other measures like air flow and cleaning efficiency....well, you can go read the 9 billion posts out there on this and decide for yourself.

-Ted