Yes, unfortunately we've done extensive research into this problem and there is not anything we can do about it. It comes down to how threading on the GPU works - there aren't any controls that we have on the driver level to throttle it in a reliable way.
I would suggest setting GPU priority to high rather than moderate to low. In our testing this will make system responsive very poor but bake times will be as fast as possible with this setting.
I would suggest keeping the AO rays setting at the lowest possible setting that delivers the quality you're after too, you can do some low resolution tests to see what settings are best before committing to a full resolution bake.
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I would suggest setting GPU priority to high rather than moderate to low. In our testing this will make system responsive very poor but bake times will be as fast as possible with this setting.
I would suggest keeping the AO rays setting at the lowest possible setting that delivers the quality you're after too, you can do some low resolution tests to see what settings are best before committing to a full resolution bake.