David, you'll probably get more opinions than you need. But in the "buy once and cry once" department I've never slept in anything better than a Western Mountaineering bag. Having owned a couple I find them to fit "snugly" which of course aids in temp rating. Little things that scream attention to detail make me like their bags. No quill feathers, good baffling to keep the insulation where it belongs, zipper air baffle that is very difficult to get stuck in the zipper, excellent ergonomics regarding both the neck and head/face closure systems. WM makes very fine bags.
I don't know anything about climbing Kilimanjaro but assuming it's expected to be a dry climb then no need to go with the Gore outer shell on the WM bag. Very good warmth to weight and bulk ratio.
A dear lady friend of ours climbed K a few years ago. And while she's uncommonly strong and healthy for her age I know if she could do it most anybody can. She said the key to her groups' success was slow and steady acclimation and almost forced hydration. Good luck!
