Get the 2x16GB kit instead of mixing sticks.

Yes, you should replace the old 2x8GB with a fresh 2x16GB 3600MHz CL16 kit. Mixing two separate kits – even if they are the same model – is a gamble on Ryzen. Memory controllers are picky, and you might end up with instability or stuck at lower speeds.

With a single 2x16GB kit, you get dual-rank sticks which help Ryzen’s performance a bit, and you know the pair is validated to work together at its rated speed. Adding another 2x8GB means four sticks, which can stress the memory controller, often forcing you to drop from 3600 to 3200 or worse. Plus, if the old kit has different ICs or timings, good luck getting it stable.

The cost difference is usually small – sell the old kit or keep it as a backup. Future you will thank you for not fighting with BIOS settings for three hours.

This is one of those “spend now to avoid headaches” deals.