Panel filter is what you get as standard. You get better flowing "after market" ones that fit the same hole.
Drilling the airbox is to allow more air in. Only ever drill the un-filtered air side of the box as you should only ever let filtered air into your engine.
Performace filters are all about allowing the air to get into your engine easier thus allowing the induction stroke to be more efficient, unfortunatly if you don't increase the flow through the exhaust you'll not get the benefits of the increased flow.
If you get the exhaust too, then the air in can happen quicker and the exhaust out can happen quicker too, which is a good thing.
