thanks, is this how it will stay or is it still WIP with netlist audio
We are constantly trying to improve on performance. But expecting 30% to increase to 100% is not realistic. The netlist subsystem (and MAME in general) do not really make use of parallel processing - for a number of good reasons to be fair.
But your core2 would not benefit from that. Running win10 with a low-performance geforce 210 has a constant resource usage as well.