If you don't get the latest Antminer, you will never get your ROI because of the difficulty increasing so fast. About every 6-10 months, Bitmain produces a new model that is at least 3-4x more powerful than the previous. According to NiceHash stats for the last year, the SHA-256 algorithm payout in BTC is regressing an average of 9% per month. So, the best plan (for max profit)would be to buy the latest antminer and plan to sell it on eBay as soon as Bitmain releases the next model. Otherwise, you'll never stay ahead of the new hashing rate spike. Other than that, you could just trade coins on bad news (I.e..China/Russia). Or, if you are lucky enough get a few new machines from Bitmain, sell them on eBay at a mark up while they are hot. On an interesting note, the Bitmain Antminer S9 and L3 have stabilized in the payout scale/rate as compared to the D3 (which came out in September). So, until they make a new Scrypt or SHA-256 ASIC machine, you can forecast your BTC payout somewhat. But the D3 (X11 algorithm) still dropping rapidly. But I'm guessing it's going to plateau at approximately the same 9% regression rate that the prior two models did. I'm hoping Bitmain will figure out how to make an ASIC machine capable of the GPU algorithms.
With BTC at about $4700..
Current S9 pays about $350/month (NiceHash) and costs $1500.
The D3 is still up around $650/mo.
L3 is around $350-$550/mo.
You can see how rapidly the hash rate, and equivalent drop in BTC payout is shown in the three charts below...
Credit for graphs from NiceHash
