Well looking at the specs on Ford's website...
http://www.ford.com/trucks/super-duty/2017/models/f450-xl/?gclid=CjwKEAiA_9nFBRCsurz7y_Px8xoSJAAUqvKCWSzE-KonSBdt1i--B1Y7C33E2OhLgkskeftj_6h7hBoCKarw_wcB&searchid=217072714|13434000754|267852822994&s_kwcid=AL!2519!3!61611883594!b!!g!!2017%20ford%20%2Bf%20%2B450%20pickup&ef_id=WKtXswAABQ2IvgrC:20170301141419:s
FAWR is the same between F350 and F450
RAWR is the same between F350 and F450 (actually F350 is higher in some cases)
Main difference is tires and brakes. F450 has 19.5" wheels and tires, and larger brakes front and rear.