Thanks dave & Jay. The 190 is on the back burner until my shipment of memory arrives. @dave, the grass paint effects converted to polygons works great.

The simple scene I created to experiment with DOF. An "infinite" plane with lots of spheres spaced equally.

Without depth of field and a sampling level of 32 gives reasonably soft shadows (Shadow softness set to 3). With depth of field turned on and even with a sampling level of 512 I still see graininess on the out of focus spheres.

It is this graininess I want to get rid of.