Ok, this one has gone somewhat past my point of imaginable render times at 01:43:10.132. I was trying for good occlusion geometry without blotching and got it in most places, except at the edges of the small card's shadow. The gap between the cards looks pretty good, though, I think.

I also tinted the sphere to verify for piz99 that light from the large sphere does reach the large card.

Whichway