Think I have said it before, but I only ever test render at the default settings and with no GI.

Secondly, I suggest setting at "the best" settings for rendering is probably often only a theory and not based on the real quality/effects that are really necessary for your true end needs.

I would tend not to change default settings other than after you have checked changes/adjustments, one by one, to justify thier usage..

Brian

bwtr