Delid, and use liquid metal (Kryonaut) *see below* instead of the rubbish TIM that sits between the CPU and the IHS.

Should see a 10-15c drop in temps.

https://www.reddit.com/r/overclocking/comments/4fw5x5/my_delid_results_i7_4790k_12c_drop/

 

I also agree on the delid advice. But the liquid metal from Thermal Grizzly is called Conductonaut (Kryonaut is their thermal paste):
https://www.overclockers.co.uk/ther...-liquid-metal-thermal-paste-1g-th-021-tg.html

 

For some more detail: the reason you're seeing uneven temperatures across cores is likely because the integrated heat spreader (IHS) on top of the CPU isn't event mounted from the factory. If you remove it (delid) and remount it properly you should see both improved temperatures, and better consistency core to core. Thermal Grizzly Conductonaut is a liquid metal that's generally the popular choice for this job (under the IHS - use normal thermal paste on top for the cooler). The majority of very high overclocks on Haswell i7s (and newer generations) use this method.

 

It's not without risk, but if you take the right precautions and you're careful, you should be ok.

Using a delid tool such as this makes the delidding part much easier:
https://www.overclockers.co.uk/der8auer-delid-die-mate-2-hs-003-dr.html
There are other tools available and some people even use a vice or razor blade, but the latter 2 options are not normally recommended.

Once you've got the IHS off, you'll want to clear off the adhesive using something relatively soft (e.g. plastic, like a credit card). Be careful not to damage any surface mount devices such as capacitors (I don't think there any on the 4790k, but just take care anyway).

You can coat the metal contacts that are near the chip with nail varnish to protect against excess liquid metal causing a short. Gamers Nexus had an article that advised using nitrocellulose based nail vanish. They also said to avoid formulations that have benzene derivates such as toluene.
https://www.gamersnexus.net/guides/3068-how-to-delid-intel-i9-cpu-and-apply-liquid-metal

When applying the liquid metal, apply less than you think you need at first, because a little can go a surprisingly long way. You can always add a little more after spreading it out. Remember to apply the liquid metal to both the chip and the part of the IHS that'll be in contact with the chip (i.e. not the side of the IHS that contacts the CPU cooler). Don't worry if you added too much liquid metal, as you can suck it back up into the original Conductonaut syringe. Isopropyl alcohol also seems to work well if you need to wipe and remove the liquid metal. Definitely watch some videos of people applying liquid metal to see the do's and don'ts. Some big don'ts are never apply liquid metal to aluminium and never use liquid metal if you're doing sub-zero (e.g. liquid nitrogen) cooling.

Lastly you may want to reseal the IHS, but this is optional.

Good luck!

 

In terms of DIY: I've done a chip myself in a vice. It went ok but I have a lot of metalwork and woodwork experience (and a good vice). I also bought a cheap delid tool from China for about £8. Worked ok, just had to wait longer for postage!

So it comes down to your confidence level. Some people also borrow, or buy then sell on their delid tool.

Intel used to solder the IHS to their CPUs until 3rd generation Core i series (Ivy Bridge). LM is too risky to be shipping and producing en masse. Whereas the normal TIM and silicone glue method is repeatable and cheap compared to LM and solder. The thermal performance of chips is good enough that Intel stuck with it. Remember that a delid is mainly to allow better overclocks, which intel isn't responsible for guaranteeing performance of...

 

For your question on whether AMD benefits from delidding, most Ryzen 1000 and 2000 series CPUs are soldered and therefore are extremely difficult (or next to impossible) to delid. However, the Ryzen 2400G and 2200G APUs use TIM and do benefit slightly from a delid (but only really recommended for people using small coolers and want to reduce fan noise).

For max operating temps, I personally don't like my CPUs to exceed 75C max and try to keep them under 70C for most of the time.

 

Ignore me, didn't realise that was an AIO.

 

I had to delid my old 4790k because the temps were crazy. I borrowed a Rockit delid tool from another forum member and once the IHS was off I found that the Intel paste had set like concrete. Once I cleaned it up and applied Coolaboratory Liquid Ultra I relidded it it using some liquid gasket on the inside of the IHS (not the edge that mates with the pcb) and left it in the relidding attachment that came with the tool overnight. Put it in the pc the next day and got a whopping 25 degrees C reduction so it was well worth doing.

Previously I had done my old 4670k. This was before any special tools were available and I used the vice and hammer method which made for a very twitchy couple of minutes. Hitting your cpu with a hammer just isn't a natural thing to do but it went ok and once I had applied liquid metal relidded with liquid gasket (same way as above) stuck it in the motherboard socket and clamped it down with my waterblock. I got 15-18 degrees C off that one.

If you buy a proper delidding tool such as the Derbauer Delid Die Mate 2 it is practically risk free and takes only seconds to remove the IHS. It also comes with a relidding kit and after you have finished using it should be able to sell it on for near enough what you paid for it.

 

This is one of the better vice delid videos, in the fact that that he doesn't use a hammer.
and he makes you aware of the SMD components (resistors/capacitors) mounted on the CPU PCB.

So if you look at delidded images of the CPU, you'll see that the SMD components (these are the bits you want to cover in nail varnish if you use liquid metal or similar) are mounted to the left of the GPU chip, when you view the writing on the IHS (integrated heat sink) the right way up.
This means that it's safer to push off the IHS from right to left. The black sealant that you see has very little give in it, so it only takes 1mm or so of sideways movement to break the seal.
Whereabouts on the planet are you, as I'm sure someone local will have a vice or delid tool.

 

Personally I'd use coloured nail polish as you can then see that there's good coverage over conductors. Sort of handy! I don't think there's conclusive evidence but people have recommended nitrocellulose... If nail polish even specifies this kind of thing. I like to let it dry at least overnight because solvents continue to evaporate for a long time during drying.

For gluing the IHS back on, I've used a dot of epoxy on each corner. This holds well but makes it easy to remove later as it's not applied all around. Some people recommend using black silicone RTV (not acid-curing) sealant. That's quite close to what Intel have used.

 

I've not heard of instances where the nail varnish caused the SMDs to overheat. Don't get it on the CPU chip though!

If you use the Mrs' nail varnish, then you'll miss out on all the fun of walking into a makeup shop and asking for nitrocellulose based (and free from benzene derivatives such as toluene) nail varnish, then receiving blank stares back from the salesperson!

Sorry, I don't have any experience with that araldite epoxy, but I've generally seen the following recommended:
- RTV silicone (aka RTV silicone gasket maker)
- UHU 46735 High-Temperature Silicone Sealant

 

Yep the Araldite is just what you want. Main difference between types is simply how long it takes to set. I don't like the 5 minute stuff as I get panicky around glue so I have 30 minute stuff.

 

To clean the old TIM off, I'd recommend using isopropyl alcohol for the cleaning solution.

The rest looks good to me.

All the best!