I run Vue 6 Pro Studio also Mark and when I use HDRI I turn the Fog and Haze from Very Low to Completely off.
Render setting quality 70%. Some will say that is too high, but I don't mind 50 hour + renders. I also use a 30% to 70% or 20% to 80% Sunlight to Ambience or somwhere in between. That way I can more control the soft shadows. I never use more than 8 to 16 sub rays and 95% Quality there.

I would rather be Politically Incorrect,
Then have Politically Correct-Incorrectness!!!