Get the matched 2x16GB kit.

Yes, the matched kit is better.

Adding two more 8GB sticks to your existing pair sounds cheaper, but it often causes headaches. Even if they’re the same brand/speed/timings, production batches vary. The memory controller has to work harder to run four sticks instead of two, and you might end up stuck at slower speeds (like 2133MHz) or get random crashes.

With a 2x16GB kit, you get two matched sticks guaranteed to work together, and you leave two slots open for future upgrades. Plus, many modern boards run better with two sticks in dual channel than four in dual-channel (consumer boards don’t support true quad-channel anyway).

Sell the old 2x8GB sticks on eBay or give them to a friend. The peace of mind is worth the extra cost.