Well, at default voltage, it should be running at 1.75...but most boards can go up to 1.85 which will help you if you want to overclock more. Just make sure your temps aren't that high, because more voltage=higher temps!
try it with the default voltage and test stability with a burnin program like prime95 or [email protected] anything that will stress the CPU to 100%. If you want you can play a graphic intense game for a few hours to test stability. If it works, and does not crash or give you an error, you dont need more voltage. If u get an error up the voltage until you stop getting the error.