Can I use 3600MHz RAM with Ryzen 5 5600X?

Yes, you can use 3600MHz RAM with Ryzen 5 5600X. Provided you set the right XMP profiles in the bios. Also, the motherboard must support overclocking. Also the Ryzen 5 5600X supports infinity fabric due to which the processor performance better with higher frequency memory.

What is the ideal CAS Latency for a RAM stick?

Lower the CAS Latency, better is the performance. CL15 RAM stick performs better than CL17 RAM stick. CAS Latency or CL is the duration of each clock cycle measured in nanoseconds.

Best RAM for Ryzen 5 5600X Builds