For example, DDR4-2400 is equivalent to PC4-19200 ... only install smaller-sized sticks in larger slots (such as a 4GB RAM stick in an 8GB slot) but also mix and match. For example, if you ...

The best RAM for ... for two 8GB sticks or one 16GB stick, you won't want less than that. In terms of speed, we'd say the sweet spot to aim for is around the 3000MHz mark for DDR4.