Also, what's your personal opinion on the worst and best difficulty levels it could be in March?
Given the types of equipment that are scheduled to ship soon, I'd put the March 2014 difficulty at about 5B. But then again, that's only if just about all manufacturers ship on time and within spec (KnC, Hashfast, CoinTerra, BFL, Bitmine, and others), especially for December orders.
Call it 3-4B conservatively, 6-7B as a ceiling.
Im not sure I can agree with that "ceiling". In the past 10 days, on average 300-350 TH was added to the network every day.
If you extrapolate that
linearly, so you assume no growth in shipping rate compared to today, 75 days x 0.35 PH = 26PH or almost another 4B difficulty, resulting in ~4-5B.
That is conservative, especially if you consider in the past 10 days, I have no clue who has been shipping or deploying this hashrate, but for sure KnC werent shipping, nor was Hashfast, Cointerra, Bitmine, ActM or any of the other soon to be released miners. Its pretty safe to assume that when they all start shipping, hashrate deployment speed will go up, by a lot compared to today. Even if it just doubles compared to today, you would be well above your ceiling.
Of course its anyone's guess if/when all those companies will actually deliver and in what volume, but for a worst case scenerario, even 10B might be a low estimate for the middle of March.