Should I get a 2x8GB kit for my Ryzen 2600?

Yes. Sell your 2x4GB kit and buy a single 2x8GB kit running 3200 or higher. The Ryzen 2600’s memory controller struggles with four sticks, and 4x4GB at 3200MHz is unreliable—you may have to drop to 2933. A fresh 2x8GB kit from a reputable brand like G.Skill, Crucial, or Corsair almost certainly hits 3200 without headaches, and leaves room to upgrade to 32GB later.