"Our second build is based on the GTX 750 Ti. This time we instead opted for 6 x 750 Ti cards for a total of $900, which is still significantly lower than the $1200 for 4 270Xs. With 6 x 750 Ti cards, the estimated GPU power draw would only be 360W, just above half of the power draw of the 270X machine. Adding in the same 75W for additional system components the total estimated power draw works out to 435W, which allows us to purchase a cheaper power supply.
At a total cost of around $1300, this machine would have a payoff period of about 97 days at the current Dogecoin rates, at 1.8MH/s"
Ok, free compy after 97 days? how is that a bad thing?
The biggest thing that hurts is that by the miners buying up multiple of these cards, they are eating up a lot of the supply, thus driving prices up for those who want to use graphics cards for gaming. If you want an AMD card right now, be prepared to pay ~$200 premium over MSRP. The sad part is, is that at that price point they are no longer competitive with Nvidia. So yes, AMD is getting great amount of sales from the miners, but as a gamer AMD is just not cost effective.
Also, keep in mind that the 97 days are where your computer is on 100% of the time only doing mining. Be prepared for fairly high electric costs, and at the end, your parts are going to be very worn out than they would be normally. So yes, you can pay off your machine (assuming the market doesn't crash and you can sell your mined coins for good value), but at the end you're left with a machine that has been overworked by most of our standards. I would never buy a second hand mining card with the intention of using it for gaming. It will have a much shorter lifespan than a second hand card used only for gaming.
But I thought Amd > Nvidia when it comes to mining..
In terms of raw performance, yes. However, the big deal with Maxwell is it's performance per watt. This means that miners can get a lot more of these, use a lower wattage power supply and have much more leniency in terms of the cooling they need for them. It saves the miners a lot in other areas.
Also, one thing to keep in mind is that these aren't Crossfire / SLI setups they're running or anything like that. Miners can have many more GPU's than what they typically allow, and hell, they can have GPU's from both AMD and Nvidia in their machines. That was something I didn't realize at first. So if somebody wants to run 1 AMD 290x and 5 GTX 750 TI's, they can do that.