Sorry but you wont make a roi in 6 months, the next difficulty jump is 13 to 17 so how do you work out 6 months to return your money?
it's already nearly 30% with 4 and 1/2 days to go.... how'd you get 13 to 17?
https://bitcoinwisdom.com/bitcoin/difficulty
Estimated Next Difficulty: 17,351,720,663 (+28.89%)
the 28.89 is the change from 13 to 17 is how much in percentage
soon to be higher
I have no clue where you are calculating this 13-17%?
Good grief - its right there in your own post - 13 billion to 17 billion ... !