Hello! This is my first time upgrading my lenovo V510-15IKB 80WQ and was wondering what speed of RAM I need, since when I run the "wmic memory chip get speed" it returns a value of 2133. Thus I'm unsure whether I need 2400 or 2666 mhz ram as the sodimm slot (image attached) when searched recommends either. Which should I buy? P.S going from 4GB to 8GB of ram, can I also mix and match different capacities of ram?