I run completely stock under the hood. If you haven't take a look at the information on K&N vs stock, do a site search.
Like this one
http://ecomodder.com/forum/showthrea...ers-11418.html
Also much information on CAI and WAI.
Best improvements for me
"Nut behind the wheel" (driving habits) see 100+ Hypermiling Tips
Limit AC use
Tire pressure