pHaze, aha.. i have same problem with 4 GPU(970-980 mixed). If pipe do not help to you, you can use one of "-w 2 --gpu-accel=2" ... "-w 2 --gpu-accel=10"
In my case it use all GPU, but speed not always full. Then you can append --gpu-loops=1024 (or similar)
This is voodoo magic
In my case it use all GPU, but speed not always full. Then you can append --gpu-loops=1024 (or similar)
This is voodoo magic