Jay shows the difference between single vs dual channel ,why should you put two ram sticks in a single channel cfg ?
At the end the conclusion is that 4 dims that act like dual rank has a slight performance increase ,but only with a high end gpu @ 1080p ,and stil depending on the ram speeds and timings ,with just two ram sticks you can always go for a higher clockspeed and better timings ,in normal circumstances ....say at least 1440p ,and i think for a 2080ti means normal on 4k the difference is not noticable .
My advice is when you having 4 ram slots and your goal is gaming ,then put 2 ram stick each of 8 GB ,when needed more capacity you always have some space left to put two modules more in there .
Like a said before , two ram sticks in dual channel cfg works perfect ,while Oster wrote "Having 4 sticks works much better performance wise than having 2"
Replace "much better" for in some scenarios slightly better performance .
Please remember that these benchmark test showing the bottleneck's with high end gpu's @ 1080p only ,at 4k wich is the 2080ti territory the gpu is always the bottleneck .