if I was you I would go medium
I’m 5’11” – and ride a large with a 70mm stem and inline post
I got the large so the top tube would rougly match the TT length on my hardtails – which are both mediums (a soul and a love/hate)
SC top tubes seem short compared to other brands – if I could afford to replace it I would get something different with a longer top tube relative to the seat tube and head tube length – the heckler fits me OK but I wouldn’t want to ride a bike any bigger and I’m taller than you. So I think you should be looking at a medium