1st you can find real answers here:
http://www.synthetic-oil-online.com/
Amsoil is the best if you want to run it. Who else stands behind extended oil changes with a real warranty? Not Mobil one for sure. Although I put Mobile one in my wife's car. And note that it's not really pure synthetic. In my X I Run Amsoil good for up to 25K miles on one Oil filter, But I change it at 15K because I am in severe service doing wheeling.
You can't beat Amsoil, The problem or weak spot with what you have is the K&N, it gets better flow for a reason, it allows more particles through, that means dirt in your oil via air intake and that's not a good thing when extending oil intervals. In fact really bad. Great for a night of racing, not for everyday, the trend now is towards the new Nanofiber technology
http://www.synthetic-oil-online.com/amsoil_air_filters.htm It's like a K&N in life span but you can clean it on the trail, it's dry no mess and has even higher flow (By way of more surface area)
You can learn a lot by visiting the site and reading and Amsoil backs all they say. You get what you pay for, That's the case with Amsoil. Mobile one is great, it you like second or 3rd best. It's off the shelf so, that's good. Only drawback on Amsoil is you order it and they ship it to your door. Is that a drawbacK? MC