Does CAS latency matter for basic productivity tasks?

No. For basic productivity — email, web browsing, Office apps, Slack — RAM capacity is what actually helps. Latency is a tuning detail for gamers and video editors. Going from 8GB to 16GB fixes a real problem, while CAS timings like CL16 vs CL18 make under a 1% real-world difference. Just buy the cheapest RAM that matches your motherboard and get more capacity.