You will notice a difference if you cut a hole in the bottom of the airbox and the filter, assuming all the snorkels have been removed. I cut the hole 1 1/4" and it made a difference. As to filters, the K&N or the UNI drop-in filters, in my opinion, the difference is negligible. You are changing a dry filter for an oil-coated filter. The "plus" is supposed to be that you save money on filters, but if you ride in a dusty environment like I do, the minus is the time and money spent on maintaining the wet filter. It needs to be cleaned, dried, and re-oiled correctly for it to work optimally. For me, it became a pia.
And, any change which increases your air intake may result in the need for rejetting the carbs so you're not running too lean, depending on the exhaust you have.
I ended up going back to the stock Triumph paper filter. I blow it out with compressed air occasionally, and change it during every oil change after I drill the hole in the bottom.....
Going with pods and eliminating the airbox is a whole 'nother ballgame.
