For the depth of field picture, my camera ( the main camera) had a focal length of 80mm and the f-stop was set at 8. Pixel samples was set to 4.
Now, I must confess that I didn't use the focus guide for this. I used semidieu's Advanced Render Options (for sale at RDNA, http://www.runtimedna.com/mod/bcs/index.php?ViewProduct=3322&vendor=semidieu ) which in the settings panel has an option to set the focal point, or even a focal point between two parts in a scene if you choose to use DoF.
I have used the focus guide in the past, it's ok, but a pain to get right involving a lot of trial and error. If I needed to focus somewhere other than the guide centre I used to set a dot in the camera dots, then using y-trans and x-trans move my object of focus to the centre of the screen, align the focus guide and then go back to my original camera setting by clicking on my saved camera view dot.
There is an easier way to set the focus distance than the guide, thanks to stewer. He wrote a python script for P5 that got the distance for you, you then copy-paste the distance into the focus dustance parameter dial, It's available here, http://www.keindesign.de/stefan/poser/dof_p5.html