Yes it is a downgrade in speed. It would show up more in speed tests than it would visually, if you used the XMP profile. However at 3600mhz the XMP is not guaranteed unless it is in the supported memory sheet for your board.
Unless you're running tests to compare the performance between the two, you almost certainly won't notice the difference.
If it's for gaming, you might squeeze a few extra frames out of it. If it's for video encoding, it could be more useful. An increase in speed is more noticeable than a decrease in latency.
Thank you, this is the kind if comments I'm looking for, I do game on my desktop machine, not competitive online games though, my kind of games are (Horizon zero dawn, witcher3, tomb raider, red dead redemption 2...) and looking to play (Elden ring and hogwart legacy, cyberpunk). I will just consider cl16 is not worth its price and hope I wont get a noticeable performance decrease.
Unless you already have the CL18 and you're switching to CL16, and you also know exactly what to look for, you won't notice a difference.
Besides, increasing the amount of memory will be much more noticeable anyway.
It's a downgrade in speed, but not a massive one. the CL16 or CL18 refers to cas latency which (greatly simplified) - is the number of clock cycles to perform certain operations, so lower is better assuming you're comparing kits with the same frequency. Ryzen chips really like low latency memory, but the difference in performance is only a few percent even with larger differences than the one you're looking at.