3600mhz at cl16 is pretty much the sweet spot though when it comes to price/performance to be honest.
The RAM has to run in a 1:1 ratio with the infinity fabric for maximum performance, and the default speed of the infinity fabric is 1800mhz (3600mhz memory is dual blabla, so it's actually 1800mhz, so perfect fit).
Most Ryzen 5xxx can, on a solid motherboard, run the infinity fabric at 1900mhz, but that means a hassle overclocking, and you'd need QVL memory that can run at 3800mhz for sure, which means dipping a lot deeper into the wallet for ~5% performance increase, if even that.
AMD has claimed new BIOS will help overclocking the infinity fabric to 2000mhz, but that is not yet tested or proven. Almost no chips can run at 2k at the moment.
Running, for example 3800mhz memory, while not overclocking the infinity fabric speed, is actually significantly slower, than running 3600mhz memory at 1:1 ratio. It's back to the old days of FSB overclocking hehe.
So, to conclude, 3600mhz is what you want. CL16 is good for that speed, anything faster than that will start costing you an arm and a leg.
I have put in order for Motherboard, 5900x and some RAM, and I went with 3600mhz CL16