For the time being, it is better to buy used 7970 cards, undervolt and under clock to mine Quark. You can reduce the memory speed to very long, around 300MHz to save electricity. Quark mining does not require memory bandwidth. It is profitable for perelectricity price up to $0.2 per kWh. I do not know how long the profit will last as it depends on the price of single coin (Shark coin, SAK). If SAK price collapse, then there is no profitable mining for most people with high electricity price.
What hashrate and power consumption (preferably at the wall) do you get?
VCore = 0.94V, core/memory = 820/250MHz, Hash = 78 MH/s. System Power from wall = 810W.
This is alomost as efficient as the GTX970 when GTX is in the low hash range. See the GTX card discussion: https://bitcointalksearch.org/topic/geforce-gtx-900-series-power-consumption-discussion-thread-1091755
That's pretty good actually, thanks.
That is from combination of 8 GPU, using 4X7990 or 3x7990+2x7970, or 2X7990+4X7970.
