I have the Celsius set and it is definitely not a "cold" weather set. I would go a size larger than you would normally wear for tree stand hunting. I have an XL set which i can fit 3-4 layers under if need be. There is not that much insulation but if you layer you wont have a problem.
I'm going to get a 90% set in the not to distant future because I'm going to start doing back country hunts in the Adirondacks again. the stuff runs a little small so if you can try it on before hand it would help I'm 6'0" and 190lbs 34" waist and 43" chest. I would say you want to be at the low end of there calculations in terms of sizing.