PowPow- Both boots are rated to -40°. The Caribus weigh slightly more than the Pacs. The Caribu also has a deeper tread on its sole, making it slightly better for off-road hikes and icy areas. . The tread on the Pacs doesn't grip as well. The Caribus' upper is a nubuck leather while these are embossed leather. I believe nubuck leather is tougher. Here is the difference between the two liners:

"ThermoPlus® InnerBoots: Pioneered by Sorel in 1993 after extensive field testing. ThermoPlus® InnerBoots provide superb warmth, moisture transfer, comfort, and durability. An advanced four-layer construction wicks perspiration from the foot, maximizes thermal insulation, and reflects body heat back to the foot for a warm, dry foot "climate".

1. Soft, short loop polyester Minktex® (green inner layer) maximizes contact to quickly wick perspiration from the foot.
2. Black polypropylene core insulates and facilitates wicking process.
3. Radiantex® foil reflects body heat back to the foot.
4. Polyester/viscose blend (camel outerlayer) insulates and stores moisture away from the foot.

Washable/Recycled InnerBoots: Pre-consumer recycled polyester. Ideal for children's boots where InnerBoots are exposed to excessive dirt and perspiration. A unique two-layer construction wicks moisture from feet and provides excellent insulation."

Probably a 6.5 in these in mens since they run a little big. I see all they have is size 7, they might be ok if your closer to a 9 in womens and are planning on thick socks and insoles.

They do run just a bit big so you could either size down just a bit or do what I did and most people end up doing.......stick with the same size and give yourself some room for thicker socks or for an extra pair of insoles when you're running thinner socks.Hope that helps.

Well these type of duck boots are all like that.The nicest I have come are across and easier to take offare the sorel conquest they sell them here.They are the best sorel has to offer as far as these type go for deep snow.I love mine

The best thing to do is shoot Backcountry.com customer support an email, or do a live chat, and ask if they can do a special order. They're great with hooking people up that way, if they're available.