Ok, so I'm bringing up this topic for a bit of discussion. I've been looking into it a bit more and the K&N air filter for the CB500 (HA-5094) seems to cost around £36 and I've been informed that it will fit the SF.
I checked the HiFlo site for their air filters to see what ones that are made for the SF fit other bikes. So having gone through the list of bikes that it also fits and checking the K&N website for air filters for those bikes I've discovered that the K&N air filter HA-0700 (which fits the CX500 and GL500i Silver Wing Interstate), should theoretically fit the SF as well since these bikes share the same HiFlo air filter which is HFA1402. The only reason I'm mentioning this is because the K&N air filter for these bikes, HA-0700 only seems to cost about £16.

Can anyone see any reason why the HA-5094 filter would be better than the HA-0700 one?

I had tried contacting K&N directly in the past and they said they'd need the original Honda Air Filter part number in order to tell me which K&N filter would be best, so does anyone know the part number?

Just trying to be as cost effective as possible here and save a few pennies when I can, you know the drill.

I had the cb 500 k&n filter and that worked fine.
According to the partslist the number of the original filter should be: 17230-my9-000

Nampus

Well a year after I'd been asking about this I've finally fitted a K&N air filter. I'd done the research and although the OE part number for the SF Air filter matched the one for the CB500 I decided to order the K&N that was stated as being for the 2000 Honda SF, HA-4020, as it was working out cheaper than the CB500 version. I can confirm that this filter fits right in the air box in place of the standard filter, and for anyone else wanting to get one I ordered mine from YB Filters online and used a wee discount code, 67264514, to get 10% off. Well chuffed. Last air filter I'll ever buy for my SuperFour.

HI
I fitted a K&N from the CB500 about 9 years ago & its fne , the only thing I needed to da was to drill off the little angled bracket that bears against the lid of the airbox that is removed to gain access to the filter & rivet it to the K&N so its held in correctly like the original.
Piston