All good processors in that list, and unless your friend is running large/heavy projects, he’s unlikely to notice a (tangible) difference. That said… here’s my 2-cent.
Regarding AMD:
I had too many bad experiences / disappointments to consider them. I’ll let others praise their glory, but for me, they are now just black-listed, no more debates about it, sorry.
Regarding Intel:
Do not target the “K” versions of i7 that are meant for over-clockers. They run warmer (…noisier) with little/no value if you don’t actually over-clock them, which I do not recommend for a Cubase workhorse.
(Slightly different story for i5 line though, since the “K” version also brings four “e-cores” to the i5 - well worth it then.)
Also look for the models with the “F” suffix that do not have the iGfx GPU, and use a separate basic NVidia GPU card (pref. fanless). The “F” versions will also save you about $25… (if you can find them in store…)
So, the (non-K) i7-12700F ends up about $100 cheaper than the 12700K, it’s about 2% slower but runs much cooler. Running cooler means slower fan (sometimes no fan at all!), which is great in a studio, esp. if you record in the same room!
In a similar line of thinking, consider even the 12700T, if you value silence over top performance.
Regarding Memory:
Since these processors support 4800MT/s DDR5… go for it!!
I would actually put my money there way before upgrading the i5-12600KF to any i7.
Actually, before talking i7 upgrades, I would even invest in a quieter chassis and PSU (a reliable high-eff. model capable of stopping its fan when running cool).
more CPU info here:
https://ark.intel.com/content/www/us/en/ark/compare.html?productIds=134594,134589,134590,134592,134595,134596