I’m 6′ with 31″ inside leg and ride a medium with a straight post and a 70mm stem.
I think the TT on the medium frame was 610mm so they are longer than a lot of mediums, so I’d say Small would suit you better.
Take their TT measurement and apply it to a current bike you are comfortable with, then work out the stem length you’d need….or make the trip up to one of their stores and ask them/ sit on a Small bike etc.
I think the Parkwood is an accomplished and worthwhile bike. I’ve been doing about 100 miles per week on mine since mid December when I built it up, and I have no adverse comment to make….and I’m not averse to making adverse comments if I think there is something adverse about a product!!!!