Kev
Which filters did you get in the end?
I was looking at two options now, the piper cross ones Ant mentions and thes from Motowheels in the states,

Looking like the OE replacements but like the look of the Motowheels ones but they dont have the swept area of the OE type.

OY,
Haven't managed to catch up with Khush lately so haven't got the new filters for the 916 yet.
As for the 998BP I will start with the OEM setup and see what I think