I put a K&N filter in my stock air box hooked to a set of ZTherapy SU's and noticed no difference during track days at two separate road tracks where my top speed exceeded 100 MPH on the straights. I'm running a 3.0 liter Rebello stroker with a free flowing exhaust. I'm pretty sure I'm intake limited. I suspect the flow limit of the SU's is more important than than the flow limits of the paper filter so going to a higher flow oiled mesh style filter does little for performance until you can get the carbs to flow better. Don't get me wrong, SU's are wonderful carbs, even on the track, but I suspect they are a biger flow restriction than the paper filter that protects them.

They begin to break down after 5 years or so. Still much cheaper than replacing paper air filters.