PLEASE NOTE: Ultimately, it is you the wearer of the dry suit that is generating the heat, the suit you choose to wear (as long as it is a neoprene suit) is simply the insulator. A membrane style of suit will offer virtually no thermal protection.
The thermal guidance information above is purely that, a guide. If you are a petite lady and feels the cold when snuggled up in bed with a winter duvet on all year round, or you are a guy that wears a T-Shirt in the depths of winter your reliance on a neoprene dry suit from a thermal perspective is at either end of the scale.