As a three day pack I've used it twice so far, up in the Western Sierras between 7-8500 ft. Scouting for deer. My 1st trip was on memorial day weekend and there was still patches of snow on the ground. Weather reports indicated it might hit freezing so we packed a bit more insulation than we initially planned for and had thought I'd need to lash stuff on the outside thinking it I did I would have been better off bringing the Zulu, but since this was my 1st weekend with the pack I wanted to give it a proper test and would make do with less than ideal gear layout.*
Being a central Californian means my view of "seasons" is a bit skewed since we only get 3 of them

Anytime water freezes at the whims of mother nature its "winter" to me.....
so what fit in there ?
HPG serape
USGI Bivy
REI trekker 1.75 wide long
USGI Poncho liner(red sack, but didn't end up needing it for the trip out)
USGI poncho (in E&E)
BDU pants XL, tri-color desert
Ltwt long tops & bottoms XL (blue stuff sack)
Spare socks (also in blue sack)
1L cook pot & lid with nesting stove)
Source ILPS hydro bladder
DIY 8L grey water bag for Sawyer set up as grav filter
Sawyer mini
2 days food in stuff sack (not pictured)
100 ft paracord & carabiner(TT H-1 pouch)
Gloves, beanie, monkey mask (other TT H-1pouch)
1L nalgene (MSM bottle holster)
A 5th of Bulliet whisky

(mini long)
That days food (other mini long)
Fire,survival,repair kits in 2x chamber pockets
Hygene and other miscellany (organizer)
TAD reccon hoodie strapped outside.
Though the fleece almost fit inside and after eating a days food on the trail it did. Looking back if I had swapped my XL sleep pad for the standard size it would have all fit inside nicely, but my mastadon sized shoulders enjoy staying of the cold ground as much as the skinny guys' do so a brought it. Tough call for comfort or Carry-ability.
On the 1st night I decided to see what this HPG Serape was made of (Sir-rap? Sarah-pee? I dunno). So I slept in my hiking shorts, short sleeve shirt with my beanie, on my trekker pad, inside the bivy sack. Temps hit 38. Not quite freezing, but cold (again, Californian-cold-weather-weanie) and I must say....I was cold !** I woke up twice just before dawn, Not freezing, not shivering, just cold. Buuuut ! Not cold enough to grab my emergency blanket or toss my fleece on, which were only 2 ft away. So I survived 38F, and at least I know what it can do. I was also able to ditch some extra insulation as I decided my long johns and fleece would be sufficient to keep me warm for sleeping the next two nights.