My 7 weeks old GA-Z97X-GAMING 3 died running Prime 95, I need RAM and cooling tips.

Run Version 26.6 of Prime 95!
Start at stock and increase Vcore and multiplier step by step and increase the multiplier one step at a time until it becomes unstable.
I would rather use 'big air' than that liquid cooler.

Stop as soon as temperature goes over 95C.

I have overclocked my i5 4690K to 4.8Ghz, with 16Gb of 2400Mhz memory (G.Skill Trident X) using a Noctua NH D15s, so that, or the even better DH15 would do. However, I got to 4.7Ghz with the same parts using the RAIJINTEK Pallas, which is a modest air cooler.

You need to understand a little more about overclocking that chip. The i7 4790K is very powerful and small, so it runs comparatively hot. If you have your cooler installed properly, your idle temperature should be around 30 degrees at 4.0Ghz. some people have reported higher idles, up to 40C, but in most cases, the backplate of their water cooler was not seated properly, or the chip was running at full Turbo Boost Speed of 4.4Ghz. From what you have said, your idle looks fine.

Using XMP profile in your BIOS will get the memory to 1.65V and 2400Mhz simply, and it will not increase their temperature much. One advantage of an air cooler is that the 'stray breeze' also cools memory and VRM on your motherboard.

Use Prime 95 Version 26.6. from here: http://www.ocaholic.ch/modules/wfdownloads/singlefile.php?cid=101&lid=758 It is a good stress test for overclocking, but does not use some instructions that super-heat the CPU.

When you get to this point run a stress test and use HWMonitor or similar to check temperatures. If they ever go over 95C stop at once. OCCT from here: http://www.ocbase.com/index.php/download is another stress test that is more gentle, and ASUS's RealBench from here http://rog.asus.com/321702014/news/realbench-v2-2-available-to-download/ is a good general benchmark and a separate 'real' stress test.

When you use automatic overclocking or software other than BIOS, it applies enough voltage to the chip to get to the desired speed in most chips, which is often more than you need for your chip.

I prefer to work the other way around. It is slower, but, for me safer.

I use the Override voltage option to set the Vcore to a reasonable, higher voltage, 1.25V, and set the multiplier to 45, and run a stress test. If everything is stable, you can increase the multiplier one step and rinse and repeat until it is unstable. THEN, increase the Voltage by 0.05V, in this case it would be to 1.30V then continue to raise the multiplier and test.

Once you have found the highest stable multiplier at a voltage under about 1.35V, reduce the voltage by 0.01, and test again. This takes quite a bit of time.

Cliff Notes version.

1. Try to find if it is stable at 4.5Ghz with 1.25v; (You need to know how much above average your chip is)
2. If passed, then increase the multiplier to by one (4.6Ghz first time around)
3. Increase Vcore by 0.01 until you get a stable result. (OCCT will detect unstable very quickly)
4. Rinse and repeat.
5. Increase 0.01v for safety. (I would not want to go over 1.35V of 24/7 use) and I would not want the Temperatures in the RealBench Benchmark to exceed 65C to 70C.

If the first test at 45 is unstable, bad luck (Turbo boost is 4.4 Ghz, so you should be able to do this).

It is a fact of mathematics that half of all chips are below average.

Once you have a stable overclock, you need to adjust the overclock mode to Adaptive and re-jigger the voltage, to get the idle voltage down to normal. Using Override means that the chip is running at that voltage all the time.

I run OCCT with one minute preparation, ten minutes of test, and five minutes of cool-off. The i7 4970K runs hot, idle 33C ish, and 60C or more in heavy use. The Cooler Master Hyper 212 EVO should run at 80C or less on an OCCT test. You can probably overclock to 4.5 or 4.6 Ghz. I'm surprised that your cooler does so poorly. Are you sure it was mounted and working properly?

If the processor was damaged, it will need more voltage to achieve a given frequency.

If you are going to go to fluid, go big. Look at the four big best, the Seidon 240, the Nepton 240, the Kraken x61 and the H-220X

Yes, the Noctua is huge, big air is huge. The smaller C14 might work. If space is an issue 'big liquid' is worth considering. Will the radiator fit in the front of your case?

I don't know about the detail differences between ASUS and Gigabyte, sorry. ASRock, I know .

If you are going to go to fluid, go big. Look at the four big best, the Seidon 240, the Nepton 240, the Kraken x61 and the H-220X

Yes, the Noctua is huge, big air is huge. The smaller C14 might work. If space is an issue 'big liquid' is worth considering. Will the radiator fit in the front of your case?

I don't know about the detail differences between ASUS and Gigabyte, sorry. ASRock, I know .