About where I was last night, I think the Min Shading Rate was 0.30 actually.  I tend to run multiple tests nudging the settings up a hair until it looks like I want.  Even rendering without IDL is spiking my CPU to 85 C or so and it will shut down on those about 1 in 4 times.

The help is appreciated.  Really, but I  tend to being conservative with settings, got in the habit when I was rendering on my old IBM T-30 laptop never saw a reason to change.