For anyone in the UK, 5800X3D is down to £389 on Scan, probably dropped in other countries too. Reportedly, AMD have dropped the price due to raptor lake. If you have AM4, now is the time.
To answer the question above some what, it’s all about the CPU having faster access to things normally stored in RAM. The more cache available to a CPU, the faster it will be. Kind of like having the kettle to make a cuppa at the side of you while flying, instead of going to the kitchen, it’s right there. I’m sure someone with a higher IQ than me can explain in more technical terms.
As for cooling I’m using a double fanned U12S from Noctua, temps are 70c when using Fenix, 75 is the highest I’ve seen so far. I’m also on a Asus B550 Gaming F motherboard, you’ll need to latest BIOS whichever board you have.