CAS 20 Ram
I don't see any cl16 available at a reasonable cost for a 20-pound jump.
It's also a solid jump in performance. CAS 17 is significantly quicker too. Or consider DDR4 3200 with a CAS 14-15 setup.
The jump from CL18 to CL16 with the R5 3600 is significant.
The variation is minor, likely around the maximum of 5%. No specific reference points available, just based on past observations.