This is another rendering with automated min-maxrad settings. Which was set to "0" on both min and max.

Finalgather rays =16000

RESULT:
The small shadows beneath the big slabs in the center, has dissappeared with the automated min-maxrad function.

So I guess these are the things that has to be taken into concideration when fiddling with a speedy final gather solution.

hmmm! I wonder what Maya put into the min-maxrad here!?!

Although I raised the final gather rays from 4000 to 16000, I cannot see ANY change in quality.

Well I'll try the 16000 ray count on the earlier solution, with min- maxrad at 1 and 10.