I know of a few, but it's not clear what several do:

-bechmark GDC_Demo (There's an XML file and folder called GDC_Demo -- don't know of any others, but maybe someone could hack the contents and XML to create one.)

-max_threads [#] (Minimum is 4 -- anything lower is ignored)

-ini_file [filename] (This file should be in your Documents\My Games\Ashes of the Singularity folder)

-gpu_profile (Unknown what it does or how to user it)

-CPUTest (Runs the CPU test I assume, instead of the regular benchmark?)

-RunLimit (Unknown -- maybe to run multiple times?)

Sadly, the Ashes_DX12.exe doesn't launch the DX12 game any longer -- you can only seem to get that by launching directly from Steam. There has to be a workaround, but I don't know it.

Edit: I found these by searching through the EXE files, and with some earlier information from StarDock (specifically, the GDC_Demo benchmark option).