Shrek,
The pad is good enough, I was going to suggest an R rating of at least 5.5 or higher.
I honestly feel you will be disappointed in the 0 degree Slick.
Go with a -20 in long wide and get a Doobie to go over the top of you. You are better off with a two layer approach rather than one, easier to control temp rating.
Remember, overheating is bad or worse than being chilled.
I don't know of any other bags on the market that are as roomy as the Kifaru Slick bag. The WM Badger and Kodiak are considered large size and are only as big as the standard Slick.
I run a 0 degree Slick and when temps hit the teens I have to layer up and throw my Woobie over the top and I still get chilled. I have heard several other people report they are off on their temps ratings a little.
Also there is nothing wrong with wearing all of your clothes to bed, including your rain gear, I've done this numerous time when it gets really cold.