Putting a GPU based renderer though some tests to see how it performs with various render killing variables applied.

In this case, it's Depth of Field.

Usually you have to really crank up the sample settings to get a clean effect and this one is no different.
Four minutes, nine seconds to render this and it's still not quite as clean as I would like it to be.

Doesn't seem like a long time but the math gets silly quickly if you consider a simple ten second animated loop.

10 second loop at 30 frames per second = 300 frames * 249 seconds per frame = 74700 seconds ( 20.75 hours )

Crazy. . . .

( is why my next machine is going to have dual GPU's in it )