Zammo, the only comment I can give you regarding size, I am 6'5" 48" chest and I have the XXXL smock, it is a great size for me, I would recomend you get a bigger size than you normaly would, not because the smocks are small, but in winter you can put it over your Swanni and all your warn base layers and be really nice and warm sat in the wind and rain just watching the wildlife go by, in summer over just a T or Bush shirt and have room for the air to move around and kep you cool.
They have a good draw cord so you can tighten it up if you need to, the othet reason for a bigger size is taking it off.
It is an art to remove said item without looking like Houdini on a bad day.
That said I would not be without mine now.