Following mining and findings performed on EVGA GeForce GTX 1070 SC GAMING Black Edition Graphics Card cards.
First run nvidia-xconfig --enable-all-gpus then set about editing the xorg.conf file to correctly set the Coolbits option.
# /etc/X11/xorg.conf
Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GTX 1070"
    BusID          "PCI:1:0:0"
    Option         "Coolbits" "28"
EndSection
Section "Device"
    Identifier     "Device1"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GTX 1070"
    BusID          "PCI:2:0:0"
    Option         "Coolbits" "28"
EndSection
Let's now apply a very light OC to the cards,
skylake:~# nvidia-settings -c :0 -q gpus
2 GPUs on skylake:0
    [0] skylake:0[gpu:0] (GeForce GTX 1070)
      Has the following names:
        GPU-0
        GPU-08ba492c-xxxx
    [1] skylake:0[gpu:1] (GeForce GTX 1070)
      Has the following names:
        GPU-1
        GPU-16e218e7-xxxx
# Apply +1300 Mhz Mem clock offset, and +100 Mhz on GPU clock
# Found these were the most stable on my Dual EVGA SC Black 1070s.
nvidia-settings -c :0 -a '[gpu:0]/GPUMemoryTransferRateOffset[3]=1300'
nvidia-settings -c :0 -a '[gpu:1]/GPUMemoryTransferRateOffset[3]=1300'
nvidia-settings -c :0 -a '[gpu:0]/GPUGraphicsClockOffset[3]=100'
nvidia-settings -c :0 -a '[gpu:1]/GPUGraphicsClockOffset[3]=100'
To check if these have applied, your X11 server needs to be running and you'll get a confirmation
~⟫ nvidia-settings -c :0 -a '[gpu:0]/GPUMemoryTransferRateOffset[3]=1400'
Failed to connect to Mir: Failed to connect to server socket: No such file or directory
Unable to init server: Could not connect: Connection refused
  Attribute 'GPUMemoryTransferRateOffset' (skylake:0[gpu:0]) assigned value 1400.
Check the final config,
skylake:~# nvidia-smi
Sat Jun 17 03:31:57 2017
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 375.66                 Driver Version: 375.66                    |
|-------------------------------+----------------------+----------------------+
| GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile Uncorr. ECC |
| Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util  Compute M. |
|===============================+======================+======================|
|   0  GeForce GTX 1070    Off  | 0000:01:00.0      On |                  N/A |
| 60%   75C    P2   146W / 151W |   2553MiB /  8112MiB |     99%      Default |
+-------------------------------+----------------------+----------------------+
|   1  GeForce GTX 1070    Off  | 0000:02:00.0     Off |                  N/A |
| 38%   66C    P2   149W / 151W |   2198MiB /  8114MiB |     99%      Default |
+-------------------------------+----------------------+----------------------+
+-----------------------------------------------------------------------------+
| Processes:                                                       GPU Memory |
|  GPU       PID  Type  Process name                               Usage      |
|=============================================================================|
|    0      1267    G   /usr/lib/xorg/Xorg                             184MiB |
|    0      3457    G   compiz                                         170MiB |
|    0      4956    C   ./ethdcrminer64                               2195MiB |
|    1      4956    C   ./ethdcrminer64                               2195MiB |
+-----------------------------------------------------------------------------+