I have the same 2017 w/ blk out pkg. Mine came with 255/40/19. I did some research on the wheels and all I could find is Ford has them and only in the original size. I wanted to do the same thing but with a wider wheel. My Ford rep also said all they showed as far as ordering them is one size in width.
I went with the RTR wheels and Nitto NT555 tires 275/40/20 fronts and 285/35/20 rear. If I had to do it again I would go with the 305/40/20 rear. Not to mention Ford wanted well over $330 a wheel. I've seen them with both 245's and 255's stock so just guessing I wouldn't go over 255's as I think they are 8.5" wide wheels.