waka (npub1pte…87jw) the number is clock cycles that it takes to fetch the data. Overall, between two kits with the same "frequency", the smaller CL number is preferrable.
https://www.tomshardware.com/reviews/cas-latency-ram-cl-timings-glossary-definition,6011.html
CL32 at 6000MT/s vs CL40 at 5200MT/s will be definitely faster. Maybe it'll give you a few percent in terms of FPS, depending on the game. If the price difference isn't great, faster memory is definitely worth it.