Over 5 Grid You received only long render.
5 is maximum. Ofcoarse for DoF higher=better
Maybe Quadric filter size 0.7 help You.....
FSAA 5 Quadric 0.7 filter size.
Here is a fast test. It's the original scene without textures. Only for make the test. The render time ins't real because I had lw on a second plane while I make the test. The test was made on a dual core 4200. I think that the scene is quite dark.
I render the same scene with the same setup in OB8 and In my last test with OB7 I have to set multiplier to 2 because the scene was too dark, now with multiplier 1 and the same setup the scene looks good.