I believe its B5 (5% biodiesel) as a max, but I'm going from memory. This owner training video will tell you all you need to know about the new 6.4L powerstroke diesel. http://www.motorcraftservice.com/vdirs/training/retail/6.4L_diesel_maintenance/superduty.html
Using the 5% bio won't void the ford warranty, ( or anyone elses ) but any failures stemming from it's use wouldn't be covered. of course, warrantys don't cover failures resulting from the use of any fuel, Here is a neat link on ford's concerns about biodiesel over 5% https://www.fleet.ford.com/showroom/environmental_vehicles/BiodieselTechnology.asp
Hmmm injectors and pumps might be the down fall there I or so I ma lead to belive. Of course with all the new 6.4 wowes that are coming out I hope that Ford pulls out of its slump and the 6.7 is a winner.