MarkAz, what is your power setup that you are running? Any idea why the price of miners has dropped so much? I am seeing S5's for $260 and S7's for $1,155?
For power I'm running either DPS-2000BB's or the IBM 2880W PSU's, both are server power supplies that require you to also get a breakout board, but there's several forum members who sell those plus high quality PCIe cables - and you get WAY more PSU for the dollar than PC power supplies. One thing I don't ever skimp on is buying power gear - you can use it from generation to generation of machine, making it a good investment, and you can pretty much resell them from what you paid, as they've already really been depreciated when we buy them (as all miners are buying the PSU's used).
As far as pricing, that's easy - miner prices are typically influenced by a combination of the price of bitcoin, the current network difficult, and the power efficiency of the miner. In your above price example, the S7 is roughly 4x the price, but 4x the hashpower - so you might think those prices are close, but the reality is they aren't. The S7 is almost 2x the efficiency, so your power cost will be 1/2 of what it would be if you had the same hashpower in S5's. So, depending on your power prices, you may not even be able to mine an S5 profitably, which is why the price has dropped.
On the difficulty side, hash power has been on a rampage, and the total network hashrate has more than doubled since October, which is pretty amazing:
https://bitcoinwisdom.com/bitcoin/difficultyLess thrilling is that means you'd be making 1/2 as much as you were back in October with the same machine.
Generally speaking, you're almost always better off going with current gen hardware, although sometimes you might find special situations where it makes sense to get something one gen back (like an S5).
