If you have a 3000 series Ryzen cpu, or prior, they do not like 4 sticks of high speed memory. Usually takes quite a bit of tampering with timings and you'll be lucky to get 3200MHz from 4 sticks.
5000 series is good with 4 sticks.
Intel is good with 4 sticks.
Both are better with 2 sticks, less wear and tear on the memory controller.
That's not including any of the adventures you may or may not get into trying to get 2 different kits to actually work together. Mixing kits has 3 results. They either work, work with tampering, don't work at all. All that is done prior at the factory by ppl with access to thousands of sticks to make a full balanced working kit, guaranteed to work. You at home have 2 extra sticks and no other recourse but RMA.
Mixing kits will most often work, sometimes fails. Crossing the street at a busy intersection, 'most often works out' means there's a very good chance of not quite making it across the street....
Your decision. Take your chances or go with the guaranteed results.