I'm looking for a new PC, so I went to part picker. One of their suggestions for my budget comes with a 2x4Gb DDR4 2400, however, in my current rig, I have 2x8Gb DDR3 1866. The motherboard on the suggestion has 4 RAM slots, so. What kind of problems, if any, would arise from having two sets of RAM installed, at different sizes, speeds, and brands?
The full rig: https://uk.pcpartpicker.com/guide/jBWG3C/modest-gaming-build
The full rig: https://uk.pcpartpicker.com/guide/jBWG3C/modest-gaming-build