I have 3 S7's from 3 different batches and mining on Kano with greater than 100% luck, none of them have broken even yet, although 2 of them are close if I do not include the PSU. But I do include the PSU in my ROI calculations since I buy them from newegg with BTC. I bought brand new EVGA 1600's for the S7's so they were somewhere around 1 BTC each at the time of purchase. So those two S7's need to generate about 1.2 BTC to break even on the miner itself plus the PSU. My 3rd S7 is further behind, it needs another half bitcoin to get caught up to the other two, so 1.7 BTC to break even on the miner plus the PSU. I expect I will probably break even on the miners by the halving but the PSU's may not get paid for for some time. I could sell the S7's at or close to break even on the miner and upgrade to S9's (just transfer the cost of the PSU's from the S7's to the S9's in my calculations) but I am with Puffy on this, it would cost more BTC then it would generate so totally not worth it at the current price. If BTC value continues to rise it may get to a point where it is worth it even at $2100 but we got a lot more value to go up before that happens. I have never purchased BTC with fiat so all of my miners are purchased with BTC I already mined going back a while now. It makes zero sense for me to buy a miner with BTC I already have that will generate less BTC than it costs. Until that calculus changes I won't be buying one of these things.
I, personally, would carry over what remains to be paid towards your PSU's to your next rig (Bitmain S9) in terms of ROI. You can sell an S7 for $250 plus buyer pays shipping right now.
However, I'm kind of having a hard time myself justifying if it's worth it right now at current price of BTC. We are at a unique time in terms of our current bullish outlook of bitcoin price compared to the previous two years of bearish markets.
We could probably conclude the buyers of the S9 may do quite well [In terms of monthly profits] during the next three to four months of a rise in bitcoin price that out paces a rise in difficulty. However, I'm speculating a bitcoin price rise as high as $1,500 the last quarter of 2016.
I'm expecting difficulty to drop down from our current 199,312,067,531 to around 187,000,000,000 by end of July and begin to increase about 5% on average every difficulty change from there until around end of August or September. I'm expecting at least one manufacturer, whether it's BitFury, KNC, or some other manufacturer, to get next generation rigs up and running soon. If another manufacturer begins adding next generation rigs to the network, we could see difficulty rises as high as 12% to 17% on average every difficulty change quite easily.
IF BTC price increases to $1,000 USD, it will have risen 72.4 percent. If difficulty increased 72.4 percent from 187,000,000,000, that would put difficulty at 322,388,000,000. When difficulty changes a certain percentage each difficulty change, it is compounded each change. For example,
If Difficulty was 187 Billion the end of July and increased 5% the first change in August, that would be 196.35 Billion with that 5 percent increase.
2 weeks later (mid August) the difficulty increases another 5% from 196.35 Billion to 206.1675 Billion.
2 weeks later (end of August) the difficulty increases another 5% from 206.1675 Billion to 216.475 Billion.
2 weeks later (mid September) the difficulty increases another 5% from 216.475 Billion to 227.299 Billion.
2 weeks later (end of September) the difficulty increases 15% from 227.299 Billion to 261.394 Billion. [I have 15% increase at this difficulty change for another manufacturer with next gen rigs coming online.]
2 weeks later (mid October) the difficulty increases 15% from 261.394 Billion to 300.604 Billion.
2 weeks later (end of October) the difficulty increases 11% from 300.604 Billion to 333.670 Billion. [This puts us above my difficulty prediction of 322,388,000,000 by end of October, 2016.]
An increase in difficulty from 187.000 Billion to 322.388 Billion is an increase of 72.4 percent.
EDIT: Looking back at the difficulty changes added up, one may think we increased 5% + 5% + 5%+ 5% + 15% + 15% + 11% = 61%. However, the way it is compounded each increase actually makes this a 72.4 percent increase.This means a projected rise in difficulty has matched a projected rise in BTC price by end of October, 2016. Which see, if the price of Bitcoin went up to $1,000 by end of October [72.4 percent increase from current price] and the difficulty is 322.388 Billion [72.4 percent increase from projected lower difficulty in July of 187 Billion].
Here is what projected earnings look like with BTC price @ $1,000 and difficulty at 322,388,000,000: Half of $655.20 (blocks halved) in a month = $327.60 (0.6552 BTC) before power costs the end of October, 2016.
EDIT: This assumes you are on a pool with low fees and 100+ percent luck. I am currently (kano.is).![](https://ip.bitcointalk.org/?u=https%3A%2F%2Fi.imgur.com%2FLvypEsa.png&t=665&c=GNh4Gew-DBGbhw)
Since our estimated ROI relies heavily upon our power costs, I'm leaving estimation of ROI up to each miner to calculate. My estimations could be wrong on the percentage difficulty increases because I'm not sure how many S9's Bitmaintech can manufacture in a month. I'm also not sure of when another manufacturer will add their next generation rigs to the network and how many they can manufacturer monthly.
All of this is pure speculation on my part. I'm offering up my speculation on difficulty for conversation among us all to determine whether it's wise to purchase the S9 or not at current price.
Projected BTC Price Movement on 3D (3-Day) Chart [Meaning each candle is 3-Days in duration]:
https://www.tradingview.com/x/tLfFQO1K//EDIT: Also, for those of you trading, I don't see this time being a pump and dump scheme. That's what the whales want you to think when they fake out a dump, only to find they have created a trap to accumulate more BTC with the intent of pumping it further afterwards. If this was a pump and dump scheme, they would have started the pump much sooner than what they did. This time we will have a pump with very little dump and continue pumping again. 2016 will be a bullish year for bitcoin. 2017 through 2019 will be even more bullish than 2016.