Overclocking beginner question

I think you have everything down. Voltage looks good. Temps are high for my taste but are still safe. Almost a full 1ghz overclock. Pretty nice

Youre all good. Just make sure temps never go above 80. If they do, tone down the overclock to help keep it cooler

Run Prime 95 with Small FFTs, this will stress the CPU the most. Blended mixes in the use of lots of RAM which results in less load on the CPU. This could result in you assuming your system is stable when in actual fact it isn't.

As for monitoring software there are some good ones out there. I am a fan of HWInfo64, however it gives information overload and there is a bit of a learning curve to get the most of it. HWMonitor is also very good and a little less complex as is Speccy. RealTemp is a great temp monitoring program if you are only interested in CPU temps.

As for temps, you are more interested in Core temps than you are with Package temps. Core temps will read higher than Package temps and they respond quicker to load changes.

Did you raise your Vcore up to that voltage to get stable, or is that still on Auto? If it's still on Auto, I would consider using either Adaptive or Offset voltage control (depends on the motherboard) and use a negative offset and try to lower your voltage. You may find that you can lower your voltage which will have a substantial affect you your temps. However if you had to raise your voltage to get stability, then disregard this.

Everything seems good. No need for offset. Temps are good and voltage is good. You have a pretty nice overclock there

To use Adaptive or Offset, look at page 2-25 of your motherboard manual. I will explain the difference between Offset and Adaptive as they are very similar. Your CPU has a VID table which tells the motherboard what voltage it needs to be stable under different thresholds of loading. Obviously while idle, the voltage is low and while fully loaded the voltage is high. There are values in between as well.

So Offset adds or subtracts the value entered in the Offset Voltage from the VID table over the entire range. This can be troublesome if you are subtracting voltage from the VID table if the offset value is too big. It may work well at the high end, but the voltage maybe too low when idle which could cause BSOD's, program crashes etc. So essentially if you are undervolting it could cause stability issues. On the other hand if you have a substantial overclock and you are adding in a lot of voltage to the VID, they you could be unnecessarily adding too much voltage when idle. While this won't cause any issues, you use more power than necessary and may make the CPU warmer at idle than necessary. This is essentially what happens when you use Static mode for 24 / 7 usage. Well except its worse in Static Mode than it is in Offset Mode.

Now Adaptive is similar to Offset, you even use the same place to enter the offset voltage and change the offset sign. Where it differs though is that it doesn't apply the offset to the entire VID range, only above a certain loading point. So at idle the CPU is still getting the voltage dictated by the VID, but it starts to add in the offset once it reaches a certain loading threshold.

Another thing to consider is the firmware that the manufacturer provides as this can have an impact on how much voltage a CPU is supplied. Most manufacturers add in their own positive offset to the VID table when in Auto. They do this to "guarantee" stability and that the system will POST. How aggressive the manufacturer is determines how warm the CPU will get when the voltage is set to Auto. I've come across Skylake CPU's in excess of 1.3V at stock (on the Z170-A motherboard from ASUS) which is quite a lot. In these cases I was able to run a negative .1V or better offset which lowered overall temps dramatically.

Since you have a starting point for stability for your overclock, most of the work is already done. I in fact use Manual or Static to dial in my Vcore. Then I use Adaptive for 24/7 usage. So for instance you have 1.27V -1.28V set for a Static Vcore, so you know that you are likely going to have to add in voltage so you would start by putting a + sign in the Offset Mode Sign. Then you would leave the offset at it's lowest value of .001V and boot up. Once in the desktop look at whatever software you use to monitor temps and voltages and look at your Vcore, then launch Prime 95 Small FFT's (make sure you are using 26.6 and nothing newer) and see where your Vcore is. Hopefully the voltage is enough to keep it from spontaneously rebooting. Note the voltage you see and subtract it from 1.28V, this is the offset you need. Stop Prime 95 (hopefully the system didn't crash in that short time) and go back into the BIOS and enter the voltage you arrived at above in to the Offset Voltage. Then reboot and test again. If you did everything right, at idle you should see something in the neighborhood of .7 - .9V and at load (Prime 95 Small FFT's) you should see 1.27 - 1.28V. If you overshot the target load Vcore than you will need to lower the value in the Offset Voltage, if you undershot, you will need to add to the Offset Voltage. Once you've dialed Vcore in, retest for stability.

This might sound complicated, but it's not really. Just a little math and a couple of reboots. The important thing is that you end up with the voltage you need at load, no more or no less, while keeping your idle voltage low. A lot of people don't care what their idle voltage is (I used to be one of them), consider that your computer is likely going to be idling 60% or more of the time it's on, why put out that heat and waste that power when you don't need to.

Good luck, update us with your results.

First off, an i5 6600K has base clock of 3.5GHz and a boost clock of 3.9GHz. What you are seeing is normal. Depending on what your motherboard defaults to will determine the clock under load. Intel has tweaked Speedstep with differing clock speeds depending on how many cores are used. So lets say you have loading on 1 - 2 cores, then Speedstep will use 3.9GHz. Now three cores might be 3.7GHz, and 4 cores will be 3.5GHz. Again this is dependent on the motherboard. I've seen a few motherboards which default to "Sync all Cores" which will utilize the boost clock (3.9GHz in your case) regardless of how many cores are loaded.

As for Vcore, you expect it to fluctuate with the load. It should go very low when idle, though not as low as you are seeing in whatever software you are using. I suspect that its an error. My son's Z87 Gryphon sometimes shows 0V at idle. This is obviously either an issue with the software we are using (HWInfo) or maybe the BIOS. Either way rest assured your CPU is getting enough voltage at idle, otherwise you would be getting BSOD's or spontaneous reboots or the computer would simply shut off.

As for the "overclocked failed" message, I've seen this on a few ASUS motherboards. Obviously I've seen it while overclocking, but I've also seen it many times with everything set to Auto. I suggest seeing if there is an updated BIOS for your board. I've heard of this in some cases with certain power supplies. I wouldn't be too concerned about this, it's more of an annoyance than an actual problem. As long as your computer is running stably, there is nothing to be concerned about.

Now as to overclocking, I would try your overclock with Vcore set to Manual or Static (whatever your motherboards term is for it) and the voltage and multiplier you were using before and stress test it. This will verify that nothing has changed as far as stability. After you are convinced that you are stable, then try following my previous instructions on how to set up Adaptive.