"washed, blocky" videos

Admin wrote:It means that your CPU is not fast enough to animate the subtitles at full speed. The usage % is of all CPU cores combined, but a single core can be a bottleneck when a task can't be divided between cores.

But it's the same CPU(i assume) with the same videos. It seems like the GTX 1060 is causing additional CPU usage through some kind of offload, or a misconfiguration, or maybe it's a driver issue in combination with Pascal GPU's(because OP's old GPU was maxwell).

The GPU should not matter at all.