I dont have that much experience overclocking either to be honest, but from reading forum posts I just lowered mine to 1.28 to start with, then 1.285, 1.29, 1.295 then finally 1.3v and my 4790k was stable at 4.65GHz.
For 4.5GHz, 1.29v should do it, depending on your silicone, maybe even lower...