Well, in my first run I let my computer use 100% CPU with 10 WUs
It's took 1h30m to complete all.
But when I limit to 50% and 5 WUs
It's took only 1h10m (2x5WUs) to complete.
Why and how?

Different Tasks require different lengths of time to complete.
Even if running exactly the same Task- Reducing the number of cores in use allows higher clocking of the CPU, and less cache contention, so less time to process each Task. But as less Tasks will be done, that will result in less work actually being done per hour.

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Grant
Darwin NT