I ride F20s. My bro rides dialogues and we both love them. i believe that when he tried on dialogues and FDBs (pretty much the same thing as F22s) they were the same size.
You don't want to get stuck with boots that are too big or else you'll be stuck on the mountain unstrapping tightening your boots and getting back on (trust me i learn this the hard way). If anything get something that is a little bit too small. at least that way it give the boots a chance too mold to your feet.