There was an interesting article a few months ago on Modular Depot about Mass Air Flow. Keep in mind this site is really technical and most of the guys over there really know their stuff. There was a lot of discussion about transfer functions, load charts, ignition and fuel tables... Bottom line is that you shouldn't change your MAF if it's not pegged (which happens around 375 rwhp). Ford units are the most consistent and easiest to tune. Any gains you may see from an aftermarket MAF could easily be obtained from a dyno tune. The stock MAF is NOT a restriction
Hope that helps