Full load means under stress or doing something. Was that screenshot taken while you were just sitting on your desktop? If so then that is NOT under load.
We cant tell you what to put them to. Overclocking is not a exact science. You have to up it a little bit, test it to make sure it is stable and then up it some more and test it again.
That way you find out what your system or card can do. It may not be the same as what someone else's card can do. So you have to trial and error it yourself.