450 is medium long, but it has adjustable drops so you can tuck it in. I think adjustable dropouts would be good for you if you're looking for drop-bar bike that can fit fat rubber. Drop bar groups have the narrower Q factor and chain line, so to fit fat tires you have to extend the chain stays a bit. No way around that.
450mm is the short cs not the long. Well I am randonneur bike my rand too and gonna go custom 29x2.3 rando gravel bike. 420 for rando and 435cs for gravel.
