I think at first I could say this, "Silicon Lottery", some chips do better than others, so you can never 100% compare one to another, so take them as reference.
VCore is king, failing generally means you need more VCore, but som other things may help as well. You can reduce or increase the ring ratio to increase the stability, as funny as it may sound some overclocks works better when you decrease the ring speed, some others when you increase. Ring voltage also me need to be toyed with for stability, if you increase, you need more volts on ring(cache in other words) wich leads to more heat, or you can actually reduce your ring(again cache) speed and lower the volts to reduce temps and have more room for giving the Vcore more juice.
Input voltage should also be checked, when you need more Vcore power, you may also need some more input voltage to keep up, mine, i keep .500v above my Vcore to keep it stable.
while bsods often means you need more VCore, hard freezes often indicates you need more input voltage or more ring voltage.
some people also mess with system agent voltage slightly and analog/digital IO voltages, slightly, but i frankly doubt you should mess with these.
lowering your RAM speed, say, to 1333mhz with command rate 2T just for testing purposes might also help. might, but just until you reach a plateau, its not preferable over just 100mhz
you can at first safely try 1.35v at 4.5 and see if it boots normally, while i personally wouldn't dare go over 1.3v, theres this... impasse whether 1.3v or 1.35v is the safe 24/7