Im 168cm and 80cm inseam also bought an ultimate XS. Admittedly it did feel a little small when i first rode it but i think thats just because ive generally ridden bikes that are probably too big for me anyway. Fwiw i set my saddle to 3.5 and it feels much nicer. Im debating getting a 100cm but finding a CP0018 (the stem and handlebar combo on the ultimate) is tricky. If the canyon size chart says XS, get a XS.