Our stallion fits a M/W - W (depending on the saddle... and how much work he's had). He has a fairly "narrow" frame for a Draft. Seems most comfortable in a SQHB if he goes western. Though he has a large shoulder - his back isn't that wide, nor is he particularly "stocky" for a draft horse. He is an 8yr old Clydesdale.
Our mare is much much wider. I actually couldn't find a treed saddle to fit her body type - she has very wide, large shoulders, with a very wide (double) back... after trying many different brands I decided to go treeless, and it works very well for her, it also allows for her changing shape and growth (she's still only 6 years old). Also a Clydesdale.