1.47 BTC for a Prisma ASICMINER 1.4Th/s+ miner. Not so sure about that research 
Power consumption is a big factor of that equation. How much power does your 1.4th/s consume?
Power consumption: ~0.67 W/G board-wise. On-wall power consumption relies on PSU
efficiency. (typically 1050-1100 W per full device, 0.75-0.78 W/G
This is the link:
https://bitcointalk.org/index.php?topic=795477.0
So it's less efficient than the S4 and you still need to buy a PSU.
Let's call 1.47BTC $600 and $100 for a PSU. That's about 50 cents a gh. I paid about 65 cents a gh on the S4, but it's more efficient. A wash maybe?
No PSU and no controller for the Prisma IMO makes the Bitmain S4 a better buy. I have been on the fence about it for a few days but the new 1250$ price closed the gap for me.
The S4 takes more electricity which kills your ROI and is more expensive. I chose the Prisma, power supplies are very inexpensive. I think in terms of ROI the Prisma is the clear winner. That's my 2 cents.
How is 0.69 W/G more than 0.75 - 0.78? Am I missing something?
EDIT: I think I was being generous when saying a PSU would be 100 bucks. You'd likely need a 1200W PSU for the Prisma which is probably 200 bucks, no?