"As the loft increases the amount they use decreases. "
Seems reasonable that if a jacket/bag/etc. were designed around the loft of down to be used, that would not be the case. Bigger baffles, loftier yet lighter down, more dead air, lighter yet warmer jacket. No? I can certainly see that the SAME garment stuffed with 650 or 850 should insulate about the same. My TNF 700fp is 'overstuffed' in my opinion, which defeats the purpose of 700 fp. It's still warm as heck.
Ye of southern climates. you fail to grok the wonderful white stuff..
White stuff means it's "warm" - because there is clouds out - see, while windy, the temperature when I took the pics on sunday was only -23C (before wind chill).
Now onthe other hand, it's now cleared off, and the sky mid-day is a bright clear sunny blue - really quite nice other than a bit of ice fog - since the temperature this morning while walking to the bus was -38C (before wind chill). Fortunately not much wind this morning.
Walking home was another story. I think it had warmed up to -32 or so, but there was some wind. I had to walk 6 blocks from the bus, and while I was warm while walking (wearing kamik boots, street clothes, heavy wool pants up over kidneys, 200 wt. fleece, that parka, toque, scarf, and mitts) I knew just from walking into the wind for a few blocks that I was underdressed for being sedentary outside at that temperature for a long period. I needed probably another wool sweater and longjohns.
phat although your temps are lower than I often see, I have been in some nasty stuff in my mountaineering gear and I must say that down bibs over long underwear with overshells (preferabley also bibs), with my Marmot 39 ounce coat (700 down - marmot model 40) are good for just about anything. <img src="/forums/images/graemlins/smirk.gif" alt="" /> I was toasty warm at -5F in a 50 mph wind for extended time. <img src="/forums/images/graemlins/laugh.gif" alt="" /> I have high top down pants too, but the bibs are the way to go.
Bibs make such a difference not just because of the extralayers over your kidneys, but they close up the thermal gap at the waist where pants and coats overlap. <img src="/forums/images/graemlins/laugh.gif" alt="" />AND they take some strain off your belly <img src="/forums/images/graemlins/blush.gif" alt="" /> by not having waist bands. <img src="/forums/images/graemlins/grin.gif" alt="" /> and they add a lot of torso insulation.
The Hood makes a tremendous difference. A really good hood is worth its weigh in gold. <img src="/forums/images/graemlins/smile.gif" alt="" />Jim <img src="/forums/images/graemlins/cool.gif" alt="" />
These are my own opinions based on wisdom earned through many wrong decisions. Your mileage may vary.