I know, my brother owned one before he bought his 16″ Five. It was too small for him and he is only 5’8″. Santa Cruz bikes are know to come up small which is why at 5’10” you would go for a large.
I was in the same situation when I was buying my Butcher, I’m 5’11 with 32 inside leg, I was just slightly to big for a Medium so went for a large as SC bike comes up quite small anyway in the TT, I run my Large with a 50mm stem and it’s perfec. I did try a Medium but thought i might struggle on it on full days out.
Think the OP should got for 17″ and I was always told you shouldn’t rely on layback posts to extend the reach as you positioning your body back further on the bike.