[Ethereum] GeForce GTX 1070 – hashrate only 680 khash/s?

You do mention that you have specified the opencl switch at start.

Did you specify -G in the ethminer parameters? This is required for ethminer to mine using your GPU. Here's the relevant ethminer --help :

Mining configuration:
-C,--cpu  When mining, use the CPU.
-G,--opencl  When mining use the GPU via OpenCL.
--opencl-platform <n>  When mining using -G/--opencl use OpenCL platform n (default: 0).
--opencl-device <n>  When mining using -G/--opencl use OpenCL device n (default: 0).
-t, --mining-threads <n> Limit number of CPU/GPU miners to n (default: use everything available on selected platform)
--allow-opencl-cpu Allows CPU to be considered as an OpenCL device if the OpenCL platform supports it.

You will get about 15 lines of messages that OpenCL is initialising if the switch works correctly - the same messages should be displayed when you are running the benchmark. Here's what it looks like:

[OPENCL]:Found suitable OpenCL device [Hawaii] with 8513388544 bytes of GPU memory
[OPENCL]:Using platform: AMD Accelerated Parallel Processing
[OPENCL]:Using device: Hawaii(OpenCL 2.0 AMD-APP (1800.11))
[OPENCL]:Printing program log
[OPENCL]:
[OPENCL]:Creating one big buffer for the DAG
[OPENCL]:Loading single big chunk kernels
[OPENCL]:Mapping one big chunk.
[OPENCL]:Creating buffer for header.
[OPENCL]:Creating mining buffer 0
[OPENCL]:Creating mining buffer 1
[OPENCL]:Printing program log
[OPENCL]:
[OPENCL]:Creating one big buffer for the DAG
[OPENCL]:Loading single big chunk kernels

Have a look on http://www.mininghwcomparison.com/list/index.php But GTX 610 is not even listed. Only GT 610 is listed with a 0.5MH/s hashrate. Nvidia cards are not good at mining, so none use it, that's why you don't find any data.