Intel Core i9-12900K CPU + MSI PRO Z690-A Mobo + CORSAIR Vengeance 32GB RAM Expired

Better memory controller (can support faster DDR5 assuming your board isn't the bottleneck) and slightly better clocks for both P-Core and E-Core and more L2 cache (24mb vs 14mb). Also E-Core clocks on 13th Gen don't interfere with the Ring clock as much as 12th Gen. But I'd say weight it with the price, a 12900K is still easier to cool than any 13th Gen. via an AIO. If you are custom looping it doesn't matter.

With a 240mm AIO my SFF with the 12900K can run Cinebench R23 fine without throttling (85C avg). But in another SFF with a 13600K it throttles like no other at stock on a 240mm AIO in Cinebench R23. Both are using contact frames. 13th Gen runs much hotter overall.

For the record also, I am using a 13900KS full custom loop with a 4090 as well for my main rig and I barely skirt by without throttling on a moderate overclock. 43.7K Cinebench R23 score but with some cores hitting 100C. Do keep that in mind when considering 13th Gen.

I feel ya, I sold my 13900K to a friend for a huge discount because I wanted to try overclocking a 13900KS (also for the better memory controller). I had assembled an open test bench for him to see that everything was in order (CPU, Mobo, RAM that I was selling for cheap). I hooked up a spare Corsair XC7 CPU block using soft tubing with an EK FLT80 D5 pump (1500L/hour) and 1 360mm RAD. I showed him that it runs as expected, ran Cinebench fine at stock stayed under 95C, 5.5GHz all core, to be honest the E-cores could be pushed to 4.5 also with no real impact to thermals too but I left it as stock. 40K R23 score.

The moment he took the setup and slapped on an Z73 Kraken 360mm AIO... it throttled hard down to 5.2/5.1 and this is with a contact frame. The score went down to 35K/36K in R23.

Not gonna feed the fanboys, let me get this out there. If the 7950X3D was out at the time I was rebuilding my main rig back in November, I would have gotten it, it wasn't so here I am with Intel and trying to solve the heat dissappation.

As to your question about how to cool the 13900K with a custom loop?
CPU Block - EK Quantum Velocity 2
Pump/Reservoir - EK Reflection 2 Distribution Block with a D5 pump for the Lian Li O11 XL
GPU Block - EK Quantum Vector 2 for the 4090 FE with Active Backplate
RAD - 3x Corsair 360mm Radiators
Tubing - Acrylic Hardline 14mm OD tubing
Contact Frame - Thermalright 12th Gen Contact Frame (works for 13th as well)
Assembled Build - https://ibb.co/JqRj9gH

For a simple setup, I just recommend you find a good CPU block that has a decent jet plate, Corsair XC7 works fine or EK Quantum Velocity 2. Get a contact frame, it generally does lower temps by at least 5C and it's only like 12 bucks. For a pump, focus on flow rate, a D5 pump is the way to go, aim for at least a 1500L/hr spec. Technically head pressure is what's needed but there's no real stat for that on product pages so we can only go by flow rate. Radiator choice doesn't matter, you only need 1 360mm if you're doing CPU only so find one that suites your aesthetics, add more if within budget or you find it saturated. Soft tubing is fine.

Lastly, thermal paste... don't focus on the raw performance numbers, you want one that performs well enough but is durable and lasts through many thermal cycles that Intel's CPUs subjects the paste to. I have literally spent hundreds of dollars on thermal pastes trying to tame 12th gen end of 2021 and now 13th Gen, it breaks conventional wisdom on thermal paste (I used to just use Artic Silver all the time decades ago). The sheer extreme thermal cycles (cold -> hot -> cold -> hot) causes the paste to either dry out or pump out.

The only 2 pastes I have seen work longer term for 12th/13th gen are:
ProlimaTech PK-3 Nano
IC Diamond (stuff lasts forever)

Ones that I have personally confirmed have degraded weeks to a month requiring a repaste:
Thermal Grizzly Kryonaut (product page says it degrades at 80C)
Thermal Grizzly Hydronaut
Artic MX-6 (may be a fluke, but I didn't test further)
Corsair XTM70
Corsair XTM50

Some of the failed pastes do have awesome thermals initially, I will admit but no longevity with 12th/13th Gen. I also have some SYY 157 on hand but have not tried it yet, supposedly lots of rave reviews. I find that the more viscous the paste, the more resistant it is to pumping out. So when you hear a review complain about how hard it is to spread the paste (I don't spread pastes btw), it might be a good indication it'll survive the thermal cycling. Direct Die cooling is also another option but I'm not brave enough to delid a CPU.

Holy hell…I was just trying to see if I should pick this up to build a gaming pc and your post made me feel like I should probably look into an old Gameboy or possibly a coloring book and some crayons. I'm pretty sure half of the words you used aren't even English but the language of some superior alien race 😂 Seriously, I greatly appreciate people like you that help guys like me make more informed decisions, even if I don't truly understand what all you said lol.