I dont think there's any reason for you to use a Black drive or even be too concerned about 5400 vs 7200. Yes its faster. No, it isn't the bottle neck in the over all throughput.
I just picked up a couple of WD Red 10TB for under $200 each. If you don't need it today, keep an eye out for what goes on sale. Stay away from the 12tb. The biggest drives always have a premium price tag associated with them, so the cost per TB is high. I paid $200 for 10tb, and the 12tb were almost $300. Insane to pay $100 for 2tb, right?
I just picked up a couple of WD Red 10TB for under $200 each. If you don't need it today, keep an eye out for what goes on sale. Stay away from the 12tb. The biggest drives always have a premium price tag associated with them, so the cost per TB is high. I paid $200 for 10tb, and the 12tb were almost $300. Insane to pay $100 for 2tb, right?