pjz you are of course an advanced user so don't be offended if this seems too challenging, I am just trying to get your basis:

is that normal for you, such a low pixel samples? Except for when I want a quick and dirty trial render, I am usually 18, 24, even over 30 to really push. Especially so when raytrace lights' min shadow bias gets down to .1 as you have it on the lights or lower.

Maybe the GI requires higher settings on pixel samples to blow out the artifacts?