In my opinion pod filters are probably not much better than running a modified airbox. If any beter at all.

I reckon the way to go is either open carbs, or mod the airbox. And by mod the airbox I mean seriously mod the airbox.

As stock the airbox is really two small chambers, but you want to chop the middle divider bit out so that you get one big airbox. Not so clever right down the bottom end of the scale, but bettertop end performance. You can run with a lid (and filter), but obviously the entry need modifying to allow maximum air but no more. Then chop the inlet rubbers down flush with the airbox and put a nice rad on them, then you get the best right through.