Nigel, I originally was just looking to eliminate the leaks and reclaim the box as storage if I could. I didn't really care about free-er flowing. Checking my mileage, it looks like the conical S&B filter may be causing too much turbulence and that's not good. I have to try a few more tanks of fuel to be sure it seems.
When the prescribed filter from K&N for stock replacement didn't seem to fit I was just curious if others would, which is why I looked at the Corvair filter. So I could buy the $35 K&N or the $10 standard paper filter to test the theory. I tried the paper and it seems to work, so a K&N probably will too. I don't care too much about more flow with the larger paper filter but I'm sure some do and it's also a good thing to know if you're stranded with a clogged filter or they're on back order.
All said, I'm thinking about getting a free flow exhaust and it seems natural to pair that with a free flow intake. So some of this research is for me and some is just for the good of the community. Plus I love screwing around in the garage with my bike whenever I get the chance
Scott