In more-than one bike I have a K&N air filter, it works well for me. I've been using 'em for >40 years. Read some online comments and they swear surgical gauze & stainless steel mesh air filters are the spawn of the devil. Clean it thoroughly with any solvent you think is safe in your workspace (better to do it outside, and with a fire extinguisher and a charged hose at-hand) blow it out, let it dry, and use a light mist of filter oil.
Sean Morley has a converted air lid box he sells. It has a reusable air filter built into it. I believe his Morley's Muscle jet kit is designed to work with it, and it's tuned for midrange, since that's where you'll spend most of your time.
The OEM box is a well-designed piece, it offers good filtration. If you have dusty conditions, leaving the OEM system in-place is not a bad way to go. Stage 7 and pod air filters can work, but you may have to spend some time with it to make things right for where you are (temperature and elevation being two considerations).
