My question would be, what's your plan for future use?
There's no point going to the expense of a WM or FF bag if it will only be used once or twice. There are plenty of quality 0* synthetic bags in the $200 range that will work.
Also, 5'10" / 200lbs... I'd recommend at least a 62" shoulder girth. And 64" will likely be better.
A 0* bag is not a very versatile bag, even with down fill. The backpacking standard is a 15-25* bag for general use, and for very good reason.
One way to get around this limited use would be to get a quality 15* or 20* bag and get a synthetic or down insulated "overbag" to extend its temp range.
I'd also bring a VBL (vapor barrier liner). That will add around 10* comfort to your bag.
A "sleeping system" is a much more sound and versatile way to go than a single use bag.
The most common mistake is to buy "too much bag"... especially on Kilimanjaro, where you'll be going through very distinct and different temp environments (quite warm at base, very cold up high), I'd prefer the versatility of a "system."
