Should I upgrade to 16GB with one 16GB stick or two 8GB sticks?

Add a second matching 8GB stick to run in dual-channel. A single 16GB stick wastes performance with single-channel memory. Dual-channel gives a 5–15% real-world boost, especially for gaming with integrated graphics or video editing. Match speed, CAS latency, and brand if possible — skipping dual-channel to save money isn’t worth it.