Should I get more RAM or tighter timings?

Get the 32GB kit with CL18 over the 16GB CL16 kit. The latency difference between CL16 and CL18 is tiny and unnoticeable in games, video editing, or daily use. Running out of memory because 16GB isn’t enough is a real problem — modern games, Chrome tabs, and background apps eat RAM. Unless you’re chasing benchmarks, take the capacity.