you can use evga precision if you want, but i would use msi afterburner. if you dont want to add voltage then dont. just keep moving the mhz up until you get artifacts. download the unigine heaven benchmark as a testing tool and let run in a loop for 20 minutes or so to see if you get any visual artifacts.
you dont have to worry about adding voltage though, it is perfectly safe with the stock bios. you may get a bit more heat and/or a bit more fan noise, but it wont hurt anything. the max stock bios vcore is already pretty low anyways and there are so many safety measures in place that nothing will get damaged.