Live in UK. Have a Kappa SV hoody for real cold and being inactive outdoors. Needed something milder for slightly warmer days and for when popping in and out of cold. Have worn this jacket for a few weeks now and its so comfortable, light and seems to regulate my temperature brilliantly. Walked the other day when it was 3 deg (38??) with t shirt underneath and was plenty warm enough. Not toasty, just right. Sides do leak a little wind/warmth but as a hot person find this nice.
As a sizing guide. I am 5'10, 175 lbs, 33' waist, 40 chest and 32.5' sleeve and Medium fit perfectly with just a t shirt underneath. possible to wear 100wt fleece underneath. A little snug under the arm, but due to softness and slight stretch to the jacket, not a problem and doesn't restrict movement. Hope this helps
N.B. I often have a problem with arms on jackets being too long. Tried on lots of softshells that felt like cardboard and looked daft in the arm. The atom (34' sleeve MED) is so soft that arms being too long is not even noticeable. Throw your fleece/softshell combination away and get one of these.
Only doubt is how durable face material would be if roughed up alot.