Have you changed your Vcore voltage, or just left it on Auto? either way, your system should boot at 4GHz, but with Voltage on Auto, it'll probably use a lot more than it needs.

What exactly IS the memory you're using? "16GB 2400" doesn't tell us much lol.

This is what I did on the first OC I did on my RIVBE/4930K, and I got my CPU to 4.2GHz stable, first shot. I set the multiplier to 42, and set a manual voltage of 1.25 - that's it! You don't need to change anything else.

1. go Into BIOS - Hit F5 to load defaults. Hit F10 to save and exit, then re-enter BIOS.
2. LEAVE EVERYHING ALONE, except... set a multiplier to 40, or 42 - whichever you want to try first. I did 42.
3. Scroll down until you find core voltage (Vcore). Set to manual, and enter a value of 1.25v in the box.
4. F10 to save, and exit. Your PC should boot to Windows no problem. - If it doesn't, go back to BIOS and try 1.3v.
5. Open CPU-Z, RealTemp, and Prime95 or other stress tester.
6. Run test for 15-30 minutes, and see if it passes. If you get any errors - workers stopping, "Instability detected" or anything other than a Pass, or test continuing error-free after this time, end the test, go back into BIOS, and set voltage to 1.3v. This should be more than it needs for even 4.2GHz, but we want to get it to pass a test first, then we can either increase the multiplier, or try and reduce the voltage, and find where it becomes unstable.

Let us know how ya go 🙂

Ah... hang on...

Did you just go down to DRAM frequency and set it to 2400? You might not be using the right DRAM voltage/timings. Does your memory have XMP?

There is always a chance that 2400MHz on the RAM could be too much for your CPU's memory controller, but it should work, seeing as you're only using 16GB of RAM. I'm on my second 4930K - the first one wouldn't run 16GB in XMP (2400MHz), in fact, it wouldn't do much of anything, and was using 1.3v on the stock - out of the box multiplier, with the memory running at 1333MHz. This was a particularly bad CPU, and I only got a replacement because Intel themselves said it wasn't right. This new one will run 64GB in XMP, but 64GB of RAM is a waste - most of it will never be used, so I'm running 32GB in XMP, with a 4.5GHz overclock @ 1.328v under load. Haven't tried to get it further yet.

It comes down to what's known as the Silicon Lottery - you either win, or you lose.

Either way, try overclocking your CPU first as I directed above. if you go into BIOS and hit F5, it'll reset all defaults, and set your RAM to 1333MHz - leave it. we want to try and get the CPU to overclock first. Once we do that, we can have a look at the memory.

Ah... hang on...

Did you just go down to DRAM frequency and set it to 2400? You might not be using the right DRAM voltage/timings. Does your memory have XMP?

There is always a chance that 2400MHz on the RAM could be too much for your CPU's memory controller, but it should work, seeing as you're only using 16GB of RAM. I'm on my second 4930K - the first one wouldn't run 16GB in XMP (2400MHz), in fact, it wouldn't do much of anything, and was using 1.3v on the stock - out of the box multiplier, with the memory running at 1333MHz. This was a particularly bad CPU, and I only got a replacement because Intel themselves said it wasn't right. This new one will run 64GB in XMP, but 64GB of RAM is a waste - most of it will never be used, so I'm running 32GB in XMP, with a 4.5GHz overclock @ 1.328v under load. Haven't tried to get it further yet.

It comes down to what's known as the Silicon Lottery - you either win, or you lose.

Either way, try overclocking your CPU first as I directed above. if you go into BIOS and hit F5, it'll reset all defaults, and set your RAM to 1333MHz - leave it. we want to try and get the CPU to overclock first. Once we do that, we can have a look at the memory.

The fluctuation in core speed you are experiancing are normal. Windows has several power options - you are probably using balanced. Windows will downclock your CPU when not under load. this is good, because the CPU can have a nice, low voltage, and run really cool when it's doing nothing. You will also have something enabled in the BIOS called "SpeedStep" This is Intels method of allowing your CPU to downclock when at idle, and boost up under load. So basically, your cpu is downclocking to 1200MHz when it's not doing anything, and should go up to 4GHz when you run Prime95, RealBench or other stress testing software.

XMP is the way to go with the memory. The XMP (Xtreme Memory Profile) has all the settings related to correct timings, voltages and frequency. This is why you are having BSOD's in Manual - the memory wasn't configured properly, and XMP does all that for you.

As for reaching 4.5GHz MINIMUM - you can probably get there, depending on how good your CPU is, but my 4930K can't hold 4.6GHz unless I go beyond 1.4v - which is beyond the "Safety limit". Unfortunately, there is no way I can tell you how high you will get; you just have to keep taking it up a bit at a time until it gets unstable. Then, try a higher voltage, and see if it fixes it. Make sure you run a stress test each time for at least 15 minutes - booting is not a good indication of stability. My CPU will boot at 4.6GHz at 1.35v, but as soon as I run RealBench it BSOD's - even at 1.4v, so it's NOT stable! If you can't get even 4.5GHz, it doesn't mean that there is anything wrong with your CPU, and there's nothing you can do about it. Some people have gotten a 4930K to 4.8GHz at ~1.428v, but mine won't do it. It's just the luck of the draw how well your CPU overclocks.
I know you have the 4960X, I'm just talking about my 4930K as a reference - the rules are the same.

Now that you have gotten to 4GHz, leave everything alone, and set the multiplier to 42 with the same voltage (1.25v) and see how it goes. remember to run the stress tester, and have RealTemp open to monitor temperatures on each core. AISuite is not what you want to be using to monitor temps. You need a more acurate monitor that reads individual CORE temperatures.

By the way, sorry if you already told us, but what cooler do you have? I'd like to know so I don't start telling you to use a voltage it can't handle.