[mars22]

Hello guys,
I am thinking about building PC which I will use mainly for openfoam. I am looking at Alder Lake CPUs and would go with DDR5. I have few questions:
1. Which CPU would you recommend between i7 12700k and i9 12900?
2. Would you consider overclocking, and if no would you still go with k version? Would then even i7 12700 be good option?

Thanks.

[flotus1]

12700k: 8 P-cores, 4 E-cores
12900k: 8 P-cores, 8 E-cores
The E-cores are pretty much useless for CFD, so you would not gain anything with the 12900k.
Overclocking these CPUs won't help much either. Thanks to various "boost" technologies and fierce competition, they operate close to maximum possible frequencies anyway.
Squeezing out a bit more performance via overclocking is quite the ordeal. You would need extremely good cooling, and probably even one of those aftermarket mounting frames for Intels new socket.

If you still want to overclock something, the better deal is probably to go with an I7-12700k, and spend the extra money on better memory. DDR5-5600 with good timings at the very least, otherwise an AMD Ryzen 5800X3D with good DDR4 memory would be faster anyway.
I'm slightly out of the loop which combination of chipset and Intel CPU allows memory overclocking. So definitely check that again before buying.

[wkernkamp]

You might wait for AMD Ryzen 7000 series with DDR5.