Hey Jules
looking for some advice just got the air box and seem to battle to fit it with the standard paper filter is it possible or should i rather convert to a foam filter now ? i have got a FMF Q4 pipe on which made a huge difference once Ive sorted the airbox and filter should i take it for remapping and then last question which filter would you suggest thanks for all your info
It does fit with the standard paper filter element, albeit tightly, which is what you want to have a good tight fit against the rubber of the filter element to keep dust out.
The performance filter box lid does a considerably better job of pre filtering the air than the stock air box lid. This will lead to longer filter life.
The KTM Instructions coming with the performance filter lid say that it should be used in conjunction with Akropovic pipe (FMF is an equivalent here) and the bike MUST be given the Akro pipe remap.
So far, I have not done the Akro remap but just did the 15 minute idle and then ignition off map rewrite.
Bike runs like a dream, with an extra pony or 2 under the new airbox lid

Yes, I would like to try a K&N type air filter element, it can only help things.