Terrible i7 6700k chip

On Auto, CPU voltage varying is normal. If you want the best overclock you'll have to set the voltage manually. Then I think you'd at least be able to hit 4.5 GHz.

Voltages have a major effect on power consumption and heat, so the temperature fluctuations may also have to do with the Auto voltage.

Maybe 1.3V to start with, and then nudge it up towards 1.35V as necessary. From that point it depends how safe you want to play it.

Personally I wouldn't to above 1.35v for all day usage, but in my opinion Id consider 1.35v for 24/7 use to be safe considering 1.45v is even considered "safe". Try running the 4.5ghz with 1.35v. If it can pass stress testing u could try for 4.6, then even 4.7 if 4.6 can pass. Whatever you do, just dont be running auto voltage for overclocking.

If you can't run 4.5ghz on 1.35v I'd like to know what your motherboard is as that could be the issue, not your 6700k.

Also if you STILL can't get 4.5ghz to run with 1.35v u could try putting it to 1.4v if you really want to achieve the stable overclock, and running a 4.5ghz stress test to see if it becomes stable, then you could try lowering your voltage a little until you hit the spot where it's stable at lowest voltage (or u could even go 4.6-4.7ghz at 1.4v as long as ur Temps remain safe and your willing to do it, then find the minimum voltage for 4.6 or 4.7 as long as 1.4v is stable). I highly doubt you'll be achieving 4.8ghz without even more volts (or unless you have a good overclocking motherboard) but you could still try if you really wanted. This will take a bit of time but if you are really wanting to hit 4.5ghz+ you can do this. Like I mentioned, on my 6600k I personally wouldn't run more than 1.35v for daily use, but even at 1.4 you are still considered in the "safe zone". It's really up to you to figure out how much your willing to push your chip to the limits with voltage, but from what I hear, as long as you don't go above 1.45v you should be safe, some people just arent willing to push that much though due to the extra heat and possibly, yes, I say again, POSSIBLY, killing your chip sooner.

Also watching your tempertures during stress testing Is very important. I don't like my cpu going above 60c, and It dosent during gaming/everyday use, but some people are alright with 80c. Realistically I say don't make the chip run over 70c on load for a long time, although this is just personal opinion and alot of people will disagree and say 80c is perfectally safe. I like to always stay on the safe side with my expensive components and that's why I don't let my 6600k ever go ahove 65c during stress testing (games are usually 5-10c lower)

If you need any help just ask, I'm not saying I'm a very experienced overclocked or very good at it, but I have enough experience to get a chip running stable at safe variables.