Paying over double MSRP just to get ~30 MH/s doesn't sound very smart to me. Especially when the next gen cards are about to be released in less than 2 months for Nvidia and 6 months for AMD. Once the new cards come out, you would be lucky to get $200 for a used RX 580.
The HD 7850 can easily get 17-18 MH/s on Ethash (<2GB Dag). Six cards will give you 108+ MH/s. You can actually get 19.5 MH/s at -ethi 4 in Claymore, but the cards will run hot. They also get 500 H/s+ on Cryptonite and 195 H/s Equihash each.
https://bitcointalk.org/index.php?topic=2520971.msg25750026#msg25750026
There are also newer cards you can use that can give you a much better ROI than paying $600 for a RX 580.
https://www.youtube.com/watch?v=Pb6B_qpr180
The HD 7850 can easily get 17-18 MH/s on Ethash (<2GB Dag). Six cards will give you 108+ MH/s. You can actually get 19.5 MH/s at -ethi 4 in Claymore, but the cards will run hot. They also get 500 H/s+ on Cryptonite and 195 H/s Equihash each.
https://bitcointalk.org/index.php?topic=2520971.msg25750026#msg25750026
There are also newer cards you can use that can give you a much better ROI than paying $600 for a RX 580.
https://www.youtube.com/watch?v=Pb6B_qpr180