I’ve got a c456, not quite the same but sizing wise I’m 6,2 with 32″ inside leg.
I’d say its a nice fit if a little short on the ups, down feels very compact and chuck able, not a gate at all. Running a 70mm stem and a slight layback seat post it’s nice in the leg but I’m off the back of the saddle slightly when climbing. Wouldn’t recommend an 18″ based in my experience, I’d prefer a smidge longer. Doesn’t look silly big, just right.
Frame itself is great geometry I’m very tempted by a ti one myself as I’m really not getting on with the carbon frame, only because I think it’s going to break any second!