I have an old gpu quadro k4000 good for editing HD but only 3 gb of memory.
I am concerned is slowing me down when displaying over 100.000 packed cubes. So I am thinking in maybe acquiring a nvidia 1080 with 11g of vram.
I know houdini does not uses multiple GPU in openCl calculations but:
How does Houdini choses which GPU to use for the viewport and openCL is it according to what monitor is connected to the card? or a preference?

There is an environment variable that can be set to tell houdini which gpu to use for opencl.

my defaults show:
HOUDINI_OCL_DEVICENUMBER = 0
HOUDINI_OCL_DEVICETYPE = ‘GPU’

You can check which CL device is active by running hpuinfo:

it would be great if you could set this in the app preferences.