So, I currently have a Coleman Peak1 sleeping bag rated for what I believe to be -10 (I forget).

I've come to realize that it's WAY to heavy. (Aprox. 7lbs!)
And actually ithe coldest i've used it in was aprox. 15*F w/30mph winds (in a tent w/fly) and I was "comfrotable". (I slept with only under garments and no socks, as I normaly over heat.)
This is my winter bag for 30*F down to the coldest of probably 10*F with wind gusts up to 50 or 60mph. (Freak weather may lead to -5 to -15 but VERY rare)[Sierra Nevadas up to 9,000FT]

So while researching new sleeping bags I've come up with the following questions.

1. Are bags rated in C or F ? None of the ratings on CampMor say *F or *C so I have no idea.
2. If a bag is rated for 0* does that mean it can be 0* in your tent or 0* outside?
3. If the bag is rated for 0* does that mean you WILL be comfortalbe (avg. person) at 0* air around your bag or does that mean you WILL survive but probably be pretty cold?
4. What type of fabric/material is good for a down bag to prevent water? My current bag is poly fill and I want to go down next as i've heard great things about their warmth as well as nwe style water-proof shells.
5. Are bags temp. rated based on the occupant being fully dressed w/beani or undergarments only.. or ?
6. How can the same brand offer a 600Fill down bag at -20* and also offer an 800Fill down bag at -20*. What exactly would the difference be as I thought the more fill the more warmth so i'm guess less quality down?
7. For my temp range of 30 down to 15 w/winds picking up every night to 10-30mph avg with gusts to 60 using a thermarest pad and sleeping in udnergarments what temp bag would you guys suggest?


My thouts are:
I like to be warm but get overheated easy, I can wear a beanie and socks for more warmth, I don't like to and WILL NOT sleep inmy clothes (unless forced to by freak storm).. so I think I would want a bag rated at probably 0* just so that I can sleep w/out full clothing and still be warm. So I'm looking at a North Face bag rated for 0* from Campmor around 3.5lbs (HALF MY WEIGHT of current baG!!) and they have 600FIll or 800Fill for SAME rating...)

What do you guys think of my plans, and does anyon ehave any for-sure answers to my questions?
I like to think I know a decent amount about sleeping bags but these more tech questions I need some assitance as I'm trying to learn more and more.

-Todd