ignore what the guy above me said. you might not notice any temp difference, but logically, less power=less heat. that saves you a couple watts, and makes your CPU last longer. get your voltage as low as you can, but thats already very good for 4.5GHz. if you see any signs of instability, bump up the voltages a tiny bit at a time till you are completely stable, then bump it up a tiny bit more just to be extra safe.
and yes, you can just run prime 95 for a couple of hours while you do whatever you want. just check for errors after.