Well the difficulty shall breach the 1 000 000 000 barrier by them, I think.
Even though the price is very good, take this in consideration.
Well you made me think of running the calculator on future possible difficulty levels. Here are the results :
1 000 000 000 8.64 a day, break even in 37 days - At this point, it is actually pretty nice
2 000 000 000 4.12 a day, break even in 77 days - At this point it seems reasonably good to me
3 000 000 000 2.68 a day, break even in 122 days - At this point I think it is a bad/useless investment.
Considering the fact that bitcoin value is always getting up, my calculations are based on $170/BTC but they will probably be actually more valuable in february.
This makes me pretty confident on this investment. I personally think (well, hope) that the difficulty won't keep this pace it has had these last months, but even if it does, there is still a pretty good margin of profitability
