Well, looks like you have hit every chat board with your experience, (advertisement?) .
The air box on the 6.7 will flow more air than you will ever need, so no advantage to change. Take the foam prefilter out during the summer, stuff it back in for winter if you want to fiddle with it.
As far as the Stealth, I'm guessing that since it leaves "all the safety parameters in place", ( which it should, considering you aren't actually changing the firmware in the ECM), that if you start encroaching on those settings it will raise a red flag during servicing. Ford knows what will and won't trigger those red flags, and will probably deny your warranty, whether the ECM has been flashed or not. Besides,elevating HP without trans tuning is pretty foolish.
Good luck.