Just the one worker, i had it pinned to 2 cores and the file took about 30 mins, pinned 6 to and it took 10 mins (file was about 3.2GB) end result was ~600mb with GPU and about 400mb with CPU (about 2.5 Hrs)
in saying that i noticed my power draw is down and the overall usage on cores is down to about 60% on 6 cores (cpu only gets 80-100%)