Do a search mate for air filters...been covered loads.
Basically, it seems to be that the best filter PERFORMANCE wise, are those that take up the least amount of room in the airbox.
Therefore either simialr to standard filters in the airtubes (I think pipercross do these also) or some that sit over the hole between the tubes and the airbox.
Flip side of this is that they are generally not as thorough at filtering as the big undertank jobbies.
Threaded Mode